perf evlist: Make {pause,resume} internal helpers

[mirror_ubuntu-jammy-kernel.git] / tools / perf / util / evlist.c

/*
 * Copyright (C) 2011, Red Hat Inc, Arnaldo Carvalho de Melo <acme@redhat.com>
 *
 * Parts came from builtin-{top,stat,record}.c, see those files for further
 * copyright notes.
 *
 * Released under the GPL v2. (and only v2, not any later version)
 */
#include "util.h"
#include <api/fs/fs.h>
#include <poll.h>
#include "cpumap.h"
#include "thread_map.h"
#include "target.h"
#include "evlist.h"
#include "evsel.h"
#include "debug.h"
#include "asm/bug.h"
#include <unistd.h>

#include "parse-events.h"
#include <subcmd/parse-options.h>

#include <sys/mman.h>

#include <linux/bitops.h>
#include <linux/hash.h>
#include <linux/log2.h>
#include <linux/err.h>

static void perf_mmap__munmap(struct perf_mmap *map);
static void perf_mmap__put(struct perf_mmap *map);

#define FD(e, x, y) (*(int *)xyarray__entry(e->fd, x, y))
#define SID(e, x, y) xyarray__entry(e->sample_id, x, y)

void perf_evlist__init(struct perf_evlist *evlist, struct cpu_map *cpus,
                       struct thread_map *threads)
{
        int i;

        for (i = 0; i < PERF_EVLIST__HLIST_SIZE; ++i)
                INIT_HLIST_HEAD(&evlist->heads[i]);
        INIT_LIST_HEAD(&evlist->entries);
        perf_evlist__set_maps(evlist, cpus, threads);
        fdarray__init(&evlist->pollfd, 64);
        evlist->workload.pid = -1;
        evlist->bkw_mmap_state = BKW_MMAP_NOTREADY;
}

struct perf_evlist *perf_evlist__new(void)
{
        struct perf_evlist *evlist = zalloc(sizeof(*evlist));

        if (evlist != NULL)
                perf_evlist__init(evlist, NULL, NULL);

        return evlist;
}

struct perf_evlist *perf_evlist__new_default(void)
{
        struct perf_evlist *evlist = perf_evlist__new();

        if (evlist && perf_evlist__add_default(evlist)) {
                perf_evlist__delete(evlist);
                evlist = NULL;
        }

        return evlist;
}

struct perf_evlist *perf_evlist__new_dummy(void)
{
        struct perf_evlist *evlist = perf_evlist__new();

        if (evlist && perf_evlist__add_dummy(evlist)) {
                perf_evlist__delete(evlist);
                evlist = NULL;
        }

        return evlist;
}

/**
 * perf_evlist__set_id_pos - set the positions of event ids.
 * @evlist: selected event list
 *
 * Events with compatible sample types all have the same id_pos
 * and is_pos.  For convenience, put a copy on evlist.
 */
void perf_evlist__set_id_pos(struct perf_evlist *evlist)
{
        struct perf_evsel *first = perf_evlist__first(evlist);

        evlist->id_pos = first->id_pos;
        evlist->is_pos = first->is_pos;
}

static void perf_evlist__update_id_pos(struct perf_evlist *evlist)
{
        struct perf_evsel *evsel;

        evlist__for_each_entry(evlist, evsel)
                perf_evsel__calc_id_pos(evsel);

        perf_evlist__set_id_pos(evlist);
}

static void perf_evlist__purge(struct perf_evlist *evlist)
{
        struct perf_evsel *pos, *n;

        evlist__for_each_entry_safe(evlist, n, pos) {
                list_del_init(&pos->node);
                pos->evlist = NULL;
                perf_evsel__delete(pos);
        }

        evlist->nr_entries = 0;
}

void perf_evlist__exit(struct perf_evlist *evlist)
{
        zfree(&evlist->mmap);
        zfree(&evlist->backward_mmap);
        fdarray__exit(&evlist->pollfd);
}

void perf_evlist__delete(struct perf_evlist *evlist)
{
        if (evlist == NULL)
                return;

        perf_evlist__munmap(evlist);
        perf_evlist__close(evlist);
        cpu_map__put(evlist->cpus);
        thread_map__put(evlist->threads);
        evlist->cpus = NULL;
        evlist->threads = NULL;
        perf_evlist__purge(evlist);
        perf_evlist__exit(evlist);
        free(evlist);
}

static void __perf_evlist__propagate_maps(struct perf_evlist *evlist,
                                          struct perf_evsel *evsel)
{
        /*
         * We already have cpus for evsel (via PMU sysfs) so
         * keep it, if there's no target cpu list defined.
         */
        if (!evsel->own_cpus || evlist->has_user_cpus) {
                cpu_map__put(evsel->cpus);
                evsel->cpus = cpu_map__get(evlist->cpus);
        } else if (evsel->cpus != evsel->own_cpus) {
                cpu_map__put(evsel->cpus);
                evsel->cpus = cpu_map__get(evsel->own_cpus);
        }

        thread_map__put(evsel->threads);
        evsel->threads = thread_map__get(evlist->threads);
}

static void perf_evlist__propagate_maps(struct perf_evlist *evlist)
{
        struct perf_evsel *evsel;

        evlist__for_each_entry(evlist, evsel)
                __perf_evlist__propagate_maps(evlist, evsel);
}

void perf_evlist__add(struct perf_evlist *evlist, struct perf_evsel *entry)
{
        entry->evlist = evlist;
        list_add_tail(&entry->node, &evlist->entries);
        entry->idx = evlist->nr_entries;
        entry->tracking = !entry->idx;

        if (!evlist->nr_entries++)
                perf_evlist__set_id_pos(evlist);

        __perf_evlist__propagate_maps(evlist, entry);
}

void perf_evlist__remove(struct perf_evlist *evlist, struct perf_evsel *evsel)
{
        evsel->evlist = NULL;
        list_del_init(&evsel->node);
        evlist->nr_entries -= 1;
}

void perf_evlist__splice_list_tail(struct perf_evlist *evlist,
                                   struct list_head *list)
{
        struct perf_evsel *evsel, *temp;

        __evlist__for_each_entry_safe(list, temp, evsel) {
                list_del_init(&evsel->node);
                perf_evlist__add(evlist, evsel);
        }
}

void __perf_evlist__set_leader(struct list_head *list)
{
        struct perf_evsel *evsel, *leader;

        leader = list_entry(list->next, struct perf_evsel, node);
        evsel = list_entry(list->prev, struct perf_evsel, node);

        leader->nr_members = evsel->idx - leader->idx + 1;

        __evlist__for_each_entry(list, evsel) {
                evsel->leader = leader;
        }
}

void perf_evlist__set_leader(struct perf_evlist *evlist)
{
        if (evlist->nr_entries) {
                evlist->nr_groups = evlist->nr_entries > 1 ? 1 : 0;
                __perf_evlist__set_leader(&evlist->entries);
        }
}

void perf_event_attr__set_max_precise_ip(struct perf_event_attr *attr)
{
        attr->precise_ip = 3;

        while (attr->precise_ip != 0) {
                int fd = sys_perf_event_open(attr, 0, -1, -1, 0);
                if (fd != -1) {
                        close(fd);
                        break;
                }
                --attr->precise_ip;
        }
}

int perf_evlist__add_default(struct perf_evlist *evlist)
{
        struct perf_event_attr attr = {
                .type = PERF_TYPE_HARDWARE,
                .config = PERF_COUNT_HW_CPU_CYCLES,
        };
        struct perf_evsel *evsel;

        event_attr_init(&attr);

        perf_event_attr__set_max_precise_ip(&attr);

        evsel = perf_evsel__new(&attr);
        if (evsel == NULL)
                goto error;

        /* use asprintf() because free(evsel) assumes name is allocated */
        if (asprintf(&evsel->name, "cycles%.*s",
                     attr.precise_ip ? attr.precise_ip + 1 : 0, ":ppp") < 0)
                goto error_free;

        perf_evlist__add(evlist, evsel);
        return 0;
error_free:
        perf_evsel__delete(evsel);
error:
        return -ENOMEM;
}

int perf_evlist__add_dummy(struct perf_evlist *evlist)
{
        struct perf_event_attr attr = {
                .type   = PERF_TYPE_SOFTWARE,
                .config = PERF_COUNT_SW_DUMMY,
                .size   = sizeof(attr), /* to capture ABI version */
        };
        struct perf_evsel *evsel = perf_evsel__new(&attr);

        if (evsel == NULL)
                return -ENOMEM;

        perf_evlist__add(evlist, evsel);
        return 0;
}

static int perf_evlist__add_attrs(struct perf_evlist *evlist,
                                  struct perf_event_attr *attrs, size_t nr_attrs)
{
        struct perf_evsel *evsel, *n;
        LIST_HEAD(head);
        size_t i;

        for (i = 0; i < nr_attrs; i++) {
                evsel = perf_evsel__new_idx(attrs + i, evlist->nr_entries + i);
                if (evsel == NULL)
                        goto out_delete_partial_list;
                list_add_tail(&evsel->node, &head);
        }

        perf_evlist__splice_list_tail(evlist, &head);

        return 0;

out_delete_partial_list:
        __evlist__for_each_entry_safe(&head, n, evsel)
                perf_evsel__delete(evsel);
        return -1;
}

int __perf_evlist__add_default_attrs(struct perf_evlist *evlist,
                                     struct perf_event_attr *attrs, size_t nr_attrs)
{
        size_t i;

        for (i = 0; i < nr_attrs; i++)
                event_attr_init(attrs + i);

        return perf_evlist__add_attrs(evlist, attrs, nr_attrs);
}

struct perf_evsel *
perf_evlist__find_tracepoint_by_id(struct perf_evlist *evlist, int id)
{
        struct perf_evsel *evsel;

        evlist__for_each_entry(evlist, evsel) {
                if (evsel->attr.type   == PERF_TYPE_TRACEPOINT &&
                    (int)evsel->attr.config == id)
                        return evsel;
        }

        return NULL;
}

struct perf_evsel *
perf_evlist__find_tracepoint_by_name(struct perf_evlist *evlist,
                                     const char *name)
{
        struct perf_evsel *evsel;

        evlist__for_each_entry(evlist, evsel) {
                if ((evsel->attr.type == PERF_TYPE_TRACEPOINT) &&
                    (strcmp(evsel->name, name) == 0))
                        return evsel;
        }

        return NULL;
}

int perf_evlist__add_newtp(struct perf_evlist *evlist,
                           const char *sys, const char *name, void *handler)
{
        struct perf_evsel *evsel = perf_evsel__newtp(sys, name);

        if (IS_ERR(evsel))
                return -1;

        evsel->handler = handler;
        perf_evlist__add(evlist, evsel);
        return 0;
}

static int perf_evlist__nr_threads(struct perf_evlist *evlist,
                                   struct perf_evsel *evsel)
{
        if (evsel->system_wide)
                return 1;
        else
                return thread_map__nr(evlist->threads);
}

void perf_evlist__disable(struct perf_evlist *evlist)
{
        struct perf_evsel *pos;

        evlist__for_each_entry(evlist, pos) {
                if (!perf_evsel__is_group_leader(pos) || !pos->fd)
                        continue;
                perf_evsel__disable(pos);
        }

        evlist->enabled = false;
}

void perf_evlist__enable(struct perf_evlist *evlist)
{
        struct perf_evsel *pos;

        evlist__for_each_entry(evlist, pos) {
                if (!perf_evsel__is_group_leader(pos) || !pos->fd)
                        continue;
                perf_evsel__enable(pos);
        }

        evlist->enabled = true;
}

void perf_evlist__toggle_enable(struct perf_evlist *evlist)
{
        (evlist->enabled ? perf_evlist__disable : perf_evlist__enable)(evlist);
}

static int perf_evlist__enable_event_cpu(struct perf_evlist *evlist,
                                         struct perf_evsel *evsel, int cpu)
{
        int thread, err;
        int nr_threads = perf_evlist__nr_threads(evlist, evsel);

        if (!evsel->fd)
                return -EINVAL;

        for (thread = 0; thread < nr_threads; thread++) {
                err = ioctl(FD(evsel, cpu, thread),
                            PERF_EVENT_IOC_ENABLE, 0);
                if (err)
                        return err;
        }
        return 0;
}

static int perf_evlist__enable_event_thread(struct perf_evlist *evlist,
                                            struct perf_evsel *evsel,
                                            int thread)
{
        int cpu, err;
        int nr_cpus = cpu_map__nr(evlist->cpus);

        if (!evsel->fd)
                return -EINVAL;

        for (cpu = 0; cpu < nr_cpus; cpu++) {
                err = ioctl(FD(evsel, cpu, thread), PERF_EVENT_IOC_ENABLE, 0);
                if (err)
                        return err;
        }
        return 0;
}

int perf_evlist__enable_event_idx(struct perf_evlist *evlist,
                                  struct perf_evsel *evsel, int idx)
{
        bool per_cpu_mmaps = !cpu_map__empty(evlist->cpus);

        if (per_cpu_mmaps)
                return perf_evlist__enable_event_cpu(evlist, evsel, idx);
        else
                return perf_evlist__enable_event_thread(evlist, evsel, idx);
}

int perf_evlist__alloc_pollfd(struct perf_evlist *evlist)
{
        int nr_cpus = cpu_map__nr(evlist->cpus);
        int nr_threads = thread_map__nr(evlist->threads);
        int nfds = 0;
        struct perf_evsel *evsel;

        evlist__for_each_entry(evlist, evsel) {
                if (evsel->system_wide)
                        nfds += nr_cpus;
                else
                        nfds += nr_cpus * nr_threads;
        }

        if (fdarray__available_entries(&evlist->pollfd) < nfds &&
            fdarray__grow(&evlist->pollfd, nfds) < 0)
                return -ENOMEM;

        return 0;
}

static int __perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd,
                                     struct perf_mmap *map, short revent)
{
        int pos = fdarray__add(&evlist->pollfd, fd, revent | POLLERR | POLLHUP);
        /*
         * Save the idx so that when we filter out fds POLLHUP'ed we can
         * close the associated evlist->mmap[] entry.
         */
        if (pos >= 0) {
                evlist->pollfd.priv[pos].ptr = map;

                fcntl(fd, F_SETFL, O_NONBLOCK);
        }

        return pos;
}

int perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd)
{
        return __perf_evlist__add_pollfd(evlist, fd, NULL, POLLIN);
}

static void perf_evlist__munmap_filtered(struct fdarray *fda, int fd,
                                         void *arg __maybe_unused)
{
        struct perf_mmap *map = fda->priv[fd].ptr;

        if (map)
                perf_mmap__put(map);
}

int perf_evlist__filter_pollfd(struct perf_evlist *evlist, short revents_and_mask)
{
        return fdarray__filter(&evlist->pollfd, revents_and_mask,
                               perf_evlist__munmap_filtered, NULL);
}

int perf_evlist__poll(struct perf_evlist *evlist, int timeout)
{
        return fdarray__poll(&evlist->pollfd, timeout);
}

static void perf_evlist__id_hash(struct perf_evlist *evlist,
                                 struct perf_evsel *evsel,
                                 int cpu, int thread, u64 id)
{
        int hash;
        struct perf_sample_id *sid = SID(evsel, cpu, thread);

        sid->id = id;
        sid->evsel = evsel;
        hash = hash_64(sid->id, PERF_EVLIST__HLIST_BITS);
        hlist_add_head(&sid->node, &evlist->heads[hash]);
}

void perf_evlist__id_add(struct perf_evlist *evlist, struct perf_evsel *evsel,
                         int cpu, int thread, u64 id)
{
        perf_evlist__id_hash(evlist, evsel, cpu, thread, id);
        evsel->id[evsel->ids++] = id;
}

int perf_evlist__id_add_fd(struct perf_evlist *evlist,
                           struct perf_evsel *evsel,
                           int cpu, int thread, int fd)
{
        u64 read_data[4] = { 0, };
        int id_idx = 1; /* The first entry is the counter value */
        u64 id;
        int ret;

        ret = ioctl(fd, PERF_EVENT_IOC_ID, &id);
        if (!ret)
                goto add;

        if (errno != ENOTTY)
                return -1;

        /* Legacy way to get event id.. All hail to old kernels! */

        /*
         * This way does not work with group format read, so bail
         * out in that case.
         */
        if (perf_evlist__read_format(evlist) & PERF_FORMAT_GROUP)
                return -1;

        if (!(evsel->attr.read_format & PERF_FORMAT_ID) ||
            read(fd, &read_data, sizeof(read_data)) == -1)
                return -1;

        if (evsel->attr.read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
                ++id_idx;
        if (evsel->attr.read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
                ++id_idx;

        id = read_data[id_idx];

 add:
        perf_evlist__id_add(evlist, evsel, cpu, thread, id);
        return 0;
}

static void perf_evlist__set_sid_idx(struct perf_evlist *evlist,
                                     struct perf_evsel *evsel, int idx, int cpu,
                                     int thread)
{
        struct perf_sample_id *sid = SID(evsel, cpu, thread);
        sid->idx = idx;
        if (evlist->cpus && cpu >= 0)
                sid->cpu = evlist->cpus->map[cpu];
        else
                sid->cpu = -1;
        if (!evsel->system_wide && evlist->threads && thread >= 0)
                sid->tid = thread_map__pid(evlist->threads, thread);
        else
                sid->tid = -1;
}

struct perf_sample_id *perf_evlist__id2sid(struct perf_evlist *evlist, u64 id)
{
        struct hlist_head *head;
        struct perf_sample_id *sid;
        int hash;

        hash = hash_64(id, PERF_EVLIST__HLIST_BITS);
        head = &evlist->heads[hash];

        hlist_for_each_entry(sid, head, node)
                if (sid->id == id)
                        return sid;

        return NULL;
}

struct perf_evsel *perf_evlist__id2evsel(struct perf_evlist *evlist, u64 id)
{
        struct perf_sample_id *sid;

        if (evlist->nr_entries == 1 || !id)
                return perf_evlist__first(evlist);

        sid = perf_evlist__id2sid(evlist, id);
        if (sid)
                return sid->evsel;

        if (!perf_evlist__sample_id_all(evlist))
                return perf_evlist__first(evlist);

        return NULL;
}

struct perf_evsel *perf_evlist__id2evsel_strict(struct perf_evlist *evlist,
                                                u64 id)
{
        struct perf_sample_id *sid;

        if (!id)
                return NULL;

        sid = perf_evlist__id2sid(evlist, id);
        if (sid)
                return sid->evsel;

        return NULL;
}

static int perf_evlist__event2id(struct perf_evlist *evlist,
                                 union perf_event *event, u64 *id)
{
        const u64 *array = event->sample.array;
        ssize_t n;

        n = (event->header.size - sizeof(event->header)) >> 3;

        if (event->header.type == PERF_RECORD_SAMPLE) {
                if (evlist->id_pos >= n)
                        return -1;
                *id = array[evlist->id_pos];
        } else {
                if (evlist->is_pos > n)
                        return -1;
                n -= evlist->is_pos;
                *id = array[n];
        }
        return 0;
}

struct perf_evsel *perf_evlist__event2evsel(struct perf_evlist *evlist,
                                            union perf_event *event)
{
        struct perf_evsel *first = perf_evlist__first(evlist);
        struct hlist_head *head;
        struct perf_sample_id *sid;
        int hash;
        u64 id;

        if (evlist->nr_entries == 1)
                return first;

        if (!first->attr.sample_id_all &&
            event->header.type != PERF_RECORD_SAMPLE)
                return first;

        if (perf_evlist__event2id(evlist, event, &id))
                return NULL;

        /* Synthesized events have an id of zero */
        if (!id)
                return first;

        hash = hash_64(id, PERF_EVLIST__HLIST_BITS);
        head = &evlist->heads[hash];

        hlist_for_each_entry(sid, head, node) {
                if (sid->id == id)
                        return sid->evsel;
        }
        return NULL;
}

static int perf_evlist__set_paused(struct perf_evlist *evlist, bool value)
{
        int i;

        if (!evlist->backward_mmap)
                return 0;

        for (i = 0; i < evlist->nr_mmaps; i++) {
                int fd = evlist->backward_mmap[i].fd;
                int err;

                if (fd < 0)
                        continue;
                err = ioctl(fd, PERF_EVENT_IOC_PAUSE_OUTPUT, value ? 1 : 0);
                if (err)
                        return err;
        }
        return 0;
}

static int perf_evlist__pause(struct perf_evlist *evlist)
{
        return perf_evlist__set_paused(evlist, true);
}

static int perf_evlist__resume(struct perf_evlist *evlist)
{
        return perf_evlist__set_paused(evlist, false);
}

/* When check_messup is true, 'end' must points to a good entry */
static union perf_event *
perf_mmap__read(struct perf_mmap *md, bool check_messup, u64 start,
                u64 end, u64 *prev)
{
        unsigned char *data = md->base + page_size;
        union perf_event *event = NULL;
        int diff = end - start;

        if (check_messup) {
                /*
                 * If we're further behind than half the buffer, there's a chance
                 * the writer will bite our tail and mess up the samples under us.
                 *
                 * If we somehow ended up ahead of the 'end', we got messed up.
                 *
                 * In either case, truncate and restart at 'end'.
                 */
                if (diff > md->mask / 2 || diff < 0) {
                        fprintf(stderr, "WARNING: failed to keep up with mmap data.\n");

                        /*
                         * 'end' points to a known good entry, start there.
                         */
                        start = end;
                        diff = 0;
                }
        }

        if (diff >= (int)sizeof(event->header)) {
                size_t size;

                event = (union perf_event *)&data[start & md->mask];
                size = event->header.size;

                if (size < sizeof(event->header) || diff < (int)size) {
                        event = NULL;
                        goto broken_event;
                }

                /*
                 * Event straddles the mmap boundary -- header should always
                 * be inside due to u64 alignment of output.
                 */
                if ((start & md->mask) + size != ((start + size) & md->mask)) {
                        unsigned int offset = start;
                        unsigned int len = min(sizeof(*event), size), cpy;
                        void *dst = md->event_copy;

                        do {
                                cpy = min(md->mask + 1 - (offset & md->mask), len);
                                memcpy(dst, &data[offset & md->mask], cpy);
                                offset += cpy;
                                dst += cpy;
                                len -= cpy;
                        } while (len);

                        event = (union perf_event *) md->event_copy;
                }

                start += size;
        }

broken_event:
        if (prev)
                *prev = start;

        return event;
}

union perf_event *perf_mmap__read_forward(struct perf_mmap *md, bool check_messup)
{
        u64 head;
        u64 old = md->prev;

        /*
         * Check if event was unmapped due to a POLLHUP/POLLERR.
         */
        if (!atomic_read(&md->refcnt))
                return NULL;

        head = perf_mmap__read_head(md);

        return perf_mmap__read(md, check_messup, old, head, &md->prev);
}

union perf_event *
perf_mmap__read_backward(struct perf_mmap *md)
{
        u64 head, end;
        u64 start = md->prev;

        /*
         * Check if event was unmapped due to a POLLHUP/POLLERR.
         */
        if (!atomic_read(&md->refcnt))
                return NULL;

        head = perf_mmap__read_head(md);
        if (!head)
                return NULL;

        /*
         * 'head' pointer starts from 0. Kernel minus sizeof(record) form
         * it each time when kernel writes to it, so in fact 'head' is
         * negative. 'end' pointer is made manually by adding the size of
         * the ring buffer to 'head' pointer, means the validate data can
         * read is the whole ring buffer. If 'end' is positive, the ring
         * buffer has not fully filled, so we must adjust 'end' to 0.
         *
         * However, since both 'head' and 'end' is unsigned, we can't
         * simply compare 'end' against 0. Here we compare '-head' and
         * the size of the ring buffer, where -head is the number of bytes
         * kernel write to the ring buffer.
         */
        if (-head < (u64)(md->mask + 1))
                end = 0;
        else
                end = head + md->mask + 1;

        return perf_mmap__read(md, false, start, end, &md->prev);
}

union perf_event *perf_evlist__mmap_read_forward(struct perf_evlist *evlist, int idx)
{
        struct perf_mmap *md = &evlist->mmap[idx];

        /*
         * Check messup is required for forward overwritable ring buffer:
         * memory pointed by md->prev can be overwritten in this case.
         * No need for read-write ring buffer: kernel stop outputting when
         * it hit md->prev (perf_mmap__consume()).
         */
        return perf_mmap__read_forward(md, evlist->overwrite);
}

union perf_event *perf_evlist__mmap_read_backward(struct perf_evlist *evlist, int idx)
{
        struct perf_mmap *md = &evlist->mmap[idx];

        /*
         * No need to check messup for backward ring buffer:
         * We can always read arbitrary long data from a backward
         * ring buffer unless we forget to pause it before reading.
         */
        return perf_mmap__read_backward(md);
}

union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
{
        return perf_evlist__mmap_read_forward(evlist, idx);
}

void perf_mmap__read_catchup(struct perf_mmap *md)
{
        u64 head;

        if (!atomic_read(&md->refcnt))
                return;

        head = perf_mmap__read_head(md);
        md->prev = head;
}

void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx)
{
        perf_mmap__read_catchup(&evlist->mmap[idx]);
}

static bool perf_mmap__empty(struct perf_mmap *md)
{
        return perf_mmap__read_head(md) == md->prev && !md->auxtrace_mmap.base;
}

static void perf_mmap__get(struct perf_mmap *map)
{
        atomic_inc(&map->refcnt);
}

static void perf_mmap__put(struct perf_mmap *md)
{
        BUG_ON(md->base && atomic_read(&md->refcnt) == 0);

        if (atomic_dec_and_test(&md->refcnt))
                perf_mmap__munmap(md);
}

void perf_mmap__consume(struct perf_mmap *md, bool overwrite)
{
        if (!overwrite) {
                u64 old = md->prev;

                perf_mmap__write_tail(md, old);
        }

        if (atomic_read(&md->refcnt) == 1 && perf_mmap__empty(md))
                perf_mmap__put(md);
}

void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx)
{
        perf_mmap__consume(&evlist->mmap[idx], evlist->overwrite);
}

int __weak auxtrace_mmap__mmap(struct auxtrace_mmap *mm __maybe_unused,
                               struct auxtrace_mmap_params *mp __maybe_unused,
                               void *userpg __maybe_unused,
                               int fd __maybe_unused)
{
        return 0;
}

void __weak auxtrace_mmap__munmap(struct auxtrace_mmap *mm __maybe_unused)
{
}

void __weak auxtrace_mmap_params__init(
                        struct auxtrace_mmap_params *mp __maybe_unused,
                        off_t auxtrace_offset __maybe_unused,
                        unsigned int auxtrace_pages __maybe_unused,
                        bool auxtrace_overwrite __maybe_unused)
{
}

void __weak auxtrace_mmap_params__set_idx(
                        struct auxtrace_mmap_params *mp __maybe_unused,
                        struct perf_evlist *evlist __maybe_unused,
                        int idx __maybe_unused,
                        bool per_cpu __maybe_unused)
{
}

static void perf_mmap__munmap(struct perf_mmap *map)
{
        if (map->base != NULL) {
                munmap(map->base, perf_mmap__mmap_len(map));
                map->base = NULL;
                map->fd = -1;
                atomic_set(&map->refcnt, 0);
        }
        auxtrace_mmap__munmap(&map->auxtrace_mmap);
}

static void perf_evlist__munmap_nofree(struct perf_evlist *evlist)
{
        int i;

        if (evlist->mmap)
                for (i = 0; i < evlist->nr_mmaps; i++)
                        perf_mmap__munmap(&evlist->mmap[i]);

        if (evlist->backward_mmap)
                for (i = 0; i < evlist->nr_mmaps; i++)
                        perf_mmap__munmap(&evlist->backward_mmap[i]);
}

void perf_evlist__munmap(struct perf_evlist *evlist)
{
        perf_evlist__munmap_nofree(evlist);
        zfree(&evlist->mmap);
        zfree(&evlist->backward_mmap);
}

static struct perf_mmap *perf_evlist__alloc_mmap(struct perf_evlist *evlist)
{
        int i;
        struct perf_mmap *map;

        evlist->nr_mmaps = cpu_map__nr(evlist->cpus);
        if (cpu_map__empty(evlist->cpus))
                evlist->nr_mmaps = thread_map__nr(evlist->threads);
        map = zalloc(evlist->nr_mmaps * sizeof(struct perf_mmap));
        if (!map)
                return NULL;

        for (i = 0; i < evlist->nr_mmaps; i++)
                map[i].fd = -1;
        return map;
}

struct mmap_params {
        int prot;
        int mask;
        struct auxtrace_mmap_params auxtrace_mp;
};

static int perf_mmap__mmap(struct perf_mmap *map,
                           struct mmap_params *mp, int fd)
{
        /*
         * The last one will be done at perf_evlist__mmap_consume(), so that we
         * make sure we don't prevent tools from consuming every last event in
         * the ring buffer.
         *
         * I.e. we can get the POLLHUP meaning that the fd doesn't exist
         * anymore, but the last events for it are still in the ring buffer,
         * waiting to be consumed.
         *
         * Tools can chose to ignore this at their own discretion, but the
         * evlist layer can't just drop it when filtering events in
         * perf_evlist__filter_pollfd().
         */
        atomic_set(&map->refcnt, 2);
        map->prev = 0;
        map->mask = mp->mask;
        map->base = mmap(NULL, perf_mmap__mmap_len(map), mp->prot,
                         MAP_SHARED, fd, 0);
        if (map->base == MAP_FAILED) {
                pr_debug2("failed to mmap perf event ring buffer, error %d\n",
                          errno);
                map->base = NULL;
                return -1;
        }
        map->fd = fd;

        if (auxtrace_mmap__mmap(&map->auxtrace_mmap,
                                &mp->auxtrace_mp, map->base, fd))
                return -1;

        return 0;
}

static bool
perf_evlist__should_poll(struct perf_evlist *evlist __maybe_unused,
                         struct perf_evsel *evsel)
{
        if (evsel->attr.write_backward)
                return false;
        return true;
}

static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx,
                                       struct mmap_params *mp, int cpu,
                                       int thread, int *_output, int *_output_backward)
{
        struct perf_evsel *evsel;
        int revent;

        evlist__for_each_entry(evlist, evsel) {
                struct perf_mmap *maps = evlist->mmap;
                int *output = _output;
                int fd;

                if (evsel->attr.write_backward) {
                        output = _output_backward;
                        maps = evlist->backward_mmap;

                        if (!maps) {
                                maps = perf_evlist__alloc_mmap(evlist);
                                if (!maps)
                                        return -1;
                                evlist->backward_mmap = maps;
                                if (evlist->bkw_mmap_state == BKW_MMAP_NOTREADY)
                                        perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_RUNNING);
                        }
                }

                if (evsel->system_wide && thread)
                        continue;

                fd = FD(evsel, cpu, thread);

                if (*output == -1) {
                        *output = fd;

                        if (perf_mmap__mmap(&maps[idx], mp, *output)  < 0)
                                return -1;
                } else {
                        if (ioctl(fd, PERF_EVENT_IOC_SET_OUTPUT, *output) != 0)
                                return -1;

                        perf_mmap__get(&maps[idx]);
                }

                revent = perf_evlist__should_poll(evlist, evsel) ? POLLIN : 0;

                /*
                 * The system_wide flag causes a selected event to be opened
                 * always without a pid.  Consequently it will never get a
                 * POLLHUP, but it is used for tracking in combination with
                 * other events, so it should not need to be polled anyway.
                 * Therefore don't add it for polling.
                 */
                if (!evsel->system_wide &&
                    __perf_evlist__add_pollfd(evlist, fd, &maps[idx], revent) < 0) {
                        perf_mmap__put(&maps[idx]);
                        return -1;
                }

                if (evsel->attr.read_format & PERF_FORMAT_ID) {
                        if (perf_evlist__id_add_fd(evlist, evsel, cpu, thread,
                                                   fd) < 0)
                                return -1;
                        perf_evlist__set_sid_idx(evlist, evsel, idx, cpu,
                                                 thread);
                }
        }

        return 0;
}

static int perf_evlist__mmap_per_cpu(struct perf_evlist *evlist,
                                     struct mmap_params *mp)
{
        int cpu, thread;
        int nr_cpus = cpu_map__nr(evlist->cpus);
        int nr_threads = thread_map__nr(evlist->threads);

        pr_debug2("perf event ring buffer mmapped per cpu\n");
        for (cpu = 0; cpu < nr_cpus; cpu++) {
                int output = -1;
                int output_backward = -1;

                auxtrace_mmap_params__set_idx(&mp->auxtrace_mp, evlist, cpu,
                                              true);

                for (thread = 0; thread < nr_threads; thread++) {
                        if (perf_evlist__mmap_per_evsel(evlist, cpu, mp, cpu,
                                                        thread, &output, &output_backward))
                                goto out_unmap;
                }
        }

        return 0;

out_unmap:
        perf_evlist__munmap_nofree(evlist);
        return -1;
}

static int perf_evlist__mmap_per_thread(struct perf_evlist *evlist,
                                        struct mmap_params *mp)
{
        int thread;
        int nr_threads = thread_map__nr(evlist->threads);

        pr_debug2("perf event ring buffer mmapped per thread\n");
        for (thread = 0; thread < nr_threads; thread++) {
                int output = -1;
                int output_backward = -1;

                auxtrace_mmap_params__set_idx(&mp->auxtrace_mp, evlist, thread,
                                              false);

                if (perf_evlist__mmap_per_evsel(evlist, thread, mp, 0, thread,
                                                &output, &output_backward))
                        goto out_unmap;
        }

        return 0;

out_unmap:
        perf_evlist__munmap_nofree(evlist);
        return -1;
}

unsigned long perf_event_mlock_kb_in_pages(void)
{
        unsigned long pages;
        int max;

        if (sysctl__read_int("kernel/perf_event_mlock_kb", &max) < 0) {
                /*
                 * Pick a once upon a time good value, i.e. things look
                 * strange since we can't read a sysctl value, but lets not
                 * die yet...
                 */
                max = 512;
        } else {
                max -= (page_size / 1024);
        }

        pages = (max * 1024) / page_size;
        if (!is_power_of_2(pages))
                pages = rounddown_pow_of_two(pages);

        return pages;
}

static size_t perf_evlist__mmap_size(unsigned long pages)
{
        if (pages == UINT_MAX)
                pages = perf_event_mlock_kb_in_pages();
        else if (!is_power_of_2(pages))
                return 0;

        return (pages + 1) * page_size;
}

static long parse_pages_arg(const char *str, unsigned long min,
                            unsigned long max)
{
        unsigned long pages, val;
        static struct parse_tag tags[] = {
                { .tag  = 'B', .mult = 1       },
                { .tag  = 'K', .mult = 1 << 10 },
                { .tag  = 'M', .mult = 1 << 20 },
                { .tag  = 'G', .mult = 1 << 30 },
                { .tag  = 0 },
        };

        if (str == NULL)
                return -EINVAL;

        val = parse_tag_value(str, tags);
        if (val != (unsigned long) -1) {
                /* we got file size value */
                pages = PERF_ALIGN(val, page_size) / page_size;
        } else {
                /* we got pages count value */
                char *eptr;
                pages = strtoul(str, &eptr, 10);
                if (*eptr != '\0')
                        return -EINVAL;
        }

        if (pages == 0 && min == 0) {
                /* leave number of pages at 0 */
        } else if (!is_power_of_2(pages)) {
                /* round pages up to next power of 2 */
                pages = roundup_pow_of_two(pages);
                if (!pages)
                        return -EINVAL;
                pr_info("rounding mmap pages size to %lu bytes (%lu pages)\n",
                        pages * page_size, pages);
        }

        if (pages > max)
                return -EINVAL;

        return pages;
}

int __perf_evlist__parse_mmap_pages(unsigned int *mmap_pages, const char *str)
{
        unsigned long max = UINT_MAX;
        long pages;

        if (max > SIZE_MAX / page_size)
                max = SIZE_MAX / page_size;

        pages = parse_pages_arg(str, 1, max);
        if (pages < 0) {
                pr_err("Invalid argument for --mmap_pages/-m\n");
                return -1;
        }

        *mmap_pages = pages;
        return 0;
}

int perf_evlist__parse_mmap_pages(const struct option *opt, const char *str,
                                  int unset __maybe_unused)
{
        return __perf_evlist__parse_mmap_pages(opt->value, str);
}

/**
 * perf_evlist__mmap_ex - Create mmaps to receive events.
 * @evlist: list of events
 * @pages: map length in pages
 * @overwrite: overwrite older events?
 * @auxtrace_pages - auxtrace map length in pages
 * @auxtrace_overwrite - overwrite older auxtrace data?
 *
 * If @overwrite is %false the user needs to signal event consumption using
 * perf_mmap__write_tail().  Using perf_evlist__mmap_read() does this
 * automatically.
 *
 * Similarly, if @auxtrace_overwrite is %false the user needs to signal data
 * consumption using auxtrace_mmap__write_tail().
 *
 * Return: %0 on success, negative error code otherwise.
 */
int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
                         bool overwrite, unsigned int auxtrace_pages,
                         bool auxtrace_overwrite)
{
        struct perf_evsel *evsel;
        const struct cpu_map *cpus = evlist->cpus;
        const struct thread_map *threads = evlist->threads;
        struct mmap_params mp = {
                .prot = PROT_READ | (overwrite ? 0 : PROT_WRITE),
        };

        if (!evlist->mmap)
                evlist->mmap = perf_evlist__alloc_mmap(evlist);
        if (!evlist->mmap)
                return -ENOMEM;

        if (evlist->pollfd.entries == NULL && perf_evlist__alloc_pollfd(evlist) < 0)
                return -ENOMEM;

        evlist->overwrite = overwrite;
        evlist->mmap_len = perf_evlist__mmap_size(pages);
        pr_debug("mmap size %zuB\n", evlist->mmap_len);
        mp.mask = evlist->mmap_len - page_size - 1;

        auxtrace_mmap_params__init(&mp.auxtrace_mp, evlist->mmap_len,
                                   auxtrace_pages, auxtrace_overwrite);

        evlist__for_each_entry(evlist, evsel) {
                if ((evsel->attr.read_format & PERF_FORMAT_ID) &&
                    evsel->sample_id == NULL &&
                    perf_evsel__alloc_id(evsel, cpu_map__nr(cpus), threads->nr) < 0)
                        return -ENOMEM;
        }

        if (cpu_map__empty(cpus))
                return perf_evlist__mmap_per_thread(evlist, &mp);

        return perf_evlist__mmap_per_cpu(evlist, &mp);
}

int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
                      bool overwrite)
{
        return perf_evlist__mmap_ex(evlist, pages, overwrite, 0, false);
}

int perf_evlist__create_maps(struct perf_evlist *evlist, struct target *target)
{
        struct cpu_map *cpus;
        struct thread_map *threads;

        threads = thread_map__new_str(target->pid, target->tid, target->uid);

        if (!threads)
                return -1;

        if (target__uses_dummy_map(target))
                cpus = cpu_map__dummy_new();
        else
                cpus = cpu_map__new(target->cpu_list);

        if (!cpus)
                goto out_delete_threads;

        evlist->has_user_cpus = !!target->cpu_list;

        perf_evlist__set_maps(evlist, cpus, threads);

        return 0;

out_delete_threads:
        thread_map__put(threads);
        return -1;
}

void perf_evlist__set_maps(struct perf_evlist *evlist, struct cpu_map *cpus,
                           struct thread_map *threads)
{
        /*
         * Allow for the possibility that one or another of the maps isn't being
         * changed i.e. don't put it.  Note we are assuming the maps that are
         * being applied are brand new and evlist is taking ownership of the
         * original reference count of 1.  If that is not the case it is up to
         * the caller to increase the reference count.
         */
        if (cpus != evlist->cpus) {
                cpu_map__put(evlist->cpus);
                evlist->cpus = cpu_map__get(cpus);
        }

        if (threads != evlist->threads) {
                thread_map__put(evlist->threads);
                evlist->threads = thread_map__get(threads);
        }

        perf_evlist__propagate_maps(evlist);
}

void __perf_evlist__set_sample_bit(struct perf_evlist *evlist,
                                   enum perf_event_sample_format bit)
{
        struct perf_evsel *evsel;

        evlist__for_each_entry(evlist, evsel)
                __perf_evsel__set_sample_bit(evsel, bit);
}

void __perf_evlist__reset_sample_bit(struct perf_evlist *evlist,
                                     enum perf_event_sample_format bit)
{
        struct perf_evsel *evsel;

        evlist__for_each_entry(evlist, evsel)
                __perf_evsel__reset_sample_bit(evsel, bit);
}

int perf_evlist__apply_filters(struct perf_evlist *evlist, struct perf_evsel **err_evsel)
{
        struct perf_evsel *evsel;
        int err = 0;
        const int ncpus = cpu_map__nr(evlist->cpus),
                  nthreads = thread_map__nr(evlist->threads);

        evlist__for_each_entry(evlist, evsel) {
                if (evsel->filter == NULL)
                        continue;

                /*
                 * filters only work for tracepoint event, which doesn't have cpu limit.
                 * So evlist and evsel should always be same.
                 */
                err = perf_evsel__apply_filter(evsel, ncpus, nthreads, evsel->filter);
                if (err) {
                        *err_evsel = evsel;
                        break;
                }
        }

        return err;
}

int perf_evlist__set_filter(struct perf_evlist *evlist, const char *filter)
{
        struct perf_evsel *evsel;
        int err = 0;

        evlist__for_each_entry(evlist, evsel) {
                if (evsel->attr.type != PERF_TYPE_TRACEPOINT)
                        continue;

                err = perf_evsel__set_filter(evsel, filter);
                if (err)
                        break;
        }

        return err;
}

int perf_evlist__set_filter_pids(struct perf_evlist *evlist, size_t npids, pid_t *pids)
{
        char *filter;
        int ret = -1;
        size_t i;

        for (i = 0; i < npids; ++i) {
                if (i == 0) {
                        if (asprintf(&filter, "common_pid != %d", pids[i]) < 0)
                                return -1;
                } else {
                        char *tmp;

                        if (asprintf(&tmp, "%s && common_pid != %d", filter, pids[i]) < 0)
                                goto out_free;

                        free(filter);
                        filter = tmp;
                }
        }

        ret = perf_evlist__set_filter(evlist, filter);
out_free:
        free(filter);
        return ret;
}

int perf_evlist__set_filter_pid(struct perf_evlist *evlist, pid_t pid)
{
        return perf_evlist__set_filter_pids(evlist, 1, &pid);
}

bool perf_evlist__valid_sample_type(struct perf_evlist *evlist)
{
        struct perf_evsel *pos;

        if (evlist->nr_entries == 1)
                return true;

        if (evlist->id_pos < 0 || evlist->is_pos < 0)
                return false;

        evlist__for_each_entry(evlist, pos) {
                if (pos->id_pos != evlist->id_pos ||
                    pos->is_pos != evlist->is_pos)
                        return false;
        }

        return true;
}

u64 __perf_evlist__combined_sample_type(struct perf_evlist *evlist)
{
        struct perf_evsel *evsel;

        if (evlist->combined_sample_type)
                return evlist->combined_sample_type;

        evlist__for_each_entry(evlist, evsel)
                evlist->combined_sample_type |= evsel->attr.sample_type;

        return evlist->combined_sample_type;
}

u64 perf_evlist__combined_sample_type(struct perf_evlist *evlist)
{
        evlist->combined_sample_type = 0;
        return __perf_evlist__combined_sample_type(evlist);
}

u64 perf_evlist__combined_branch_type(struct perf_evlist *evlist)
{
        struct perf_evsel *evsel;
        u64 branch_type = 0;

        evlist__for_each_entry(evlist, evsel)
                branch_type |= evsel->attr.branch_sample_type;
        return branch_type;
}

bool perf_evlist__valid_read_format(struct perf_evlist *evlist)
{
        struct perf_evsel *first = perf_evlist__first(evlist), *pos = first;
        u64 read_format = first->attr.read_format;
        u64 sample_type = first->attr.sample_type;

        evlist__for_each_entry(evlist, pos) {
                if (read_format != pos->attr.read_format)
                        return false;
        }

        /* PERF_SAMPLE_READ imples PERF_FORMAT_ID. */
        if ((sample_type & PERF_SAMPLE_READ) &&
            !(read_format & PERF_FORMAT_ID)) {
                return false;
        }

        return true;
}

u64 perf_evlist__read_format(struct perf_evlist *evlist)
{
        struct perf_evsel *first = perf_evlist__first(evlist);
        return first->attr.read_format;
}

u16 perf_evlist__id_hdr_size(struct perf_evlist *evlist)
{
        struct perf_evsel *first = perf_evlist__first(evlist);
        struct perf_sample *data;
        u64 sample_type;
        u16 size = 0;

        if (!first->attr.sample_id_all)
                goto out;

        sample_type = first->attr.sample_type;

        if (sample_type & PERF_SAMPLE_TID)
                size += sizeof(data->tid) * 2;

       if (sample_type & PERF_SAMPLE_TIME)
                size += sizeof(data->time);

        if (sample_type & PERF_SAMPLE_ID)
                size += sizeof(data->id);

        if (sample_type & PERF_SAMPLE_STREAM_ID)
                size += sizeof(data->stream_id);

        if (sample_type & PERF_SAMPLE_CPU)
                size += sizeof(data->cpu) * 2;

        if (sample_type & PERF_SAMPLE_IDENTIFIER)
                size += sizeof(data->id);
out:
        return size;
}

bool perf_evlist__valid_sample_id_all(struct perf_evlist *evlist)
{
        struct perf_evsel *first = perf_evlist__first(evlist), *pos = first;

        evlist__for_each_entry_continue(evlist, pos) {
                if (first->attr.sample_id_all != pos->attr.sample_id_all)
                        return false;
        }

        return true;
}

bool perf_evlist__sample_id_all(struct perf_evlist *evlist)
{
        struct perf_evsel *first = perf_evlist__first(evlist);
        return first->attr.sample_id_all;
}

void perf_evlist__set_selected(struct perf_evlist *evlist,
                               struct perf_evsel *evsel)
{
        evlist->selected = evsel;
}

void perf_evlist__close(struct perf_evlist *evlist)
{
        struct perf_evsel *evsel;
        int ncpus = cpu_map__nr(evlist->cpus);
        int nthreads = thread_map__nr(evlist->threads);
        int n;

        evlist__for_each_entry_reverse(evlist, evsel) {
                n = evsel->cpus ? evsel->cpus->nr : ncpus;
                perf_evsel__close(evsel, n, nthreads);
        }
}

static int perf_evlist__create_syswide_maps(struct perf_evlist *evlist)
{
        struct cpu_map    *cpus;
        struct thread_map *threads;
        int err = -ENOMEM;

        /*
         * Try reading /sys/devices/system/cpu/online to get
         * an all cpus map.
         *
         * FIXME: -ENOMEM is the best we can do here, the cpu_map
         * code needs an overhaul to properly forward the
         * error, and we may not want to do that fallback to a
         * default cpu identity map :-\
         */
        cpus = cpu_map__new(NULL);
        if (!cpus)
                goto out;

        threads = thread_map__new_dummy();
        if (!threads)
                goto out_put;

        perf_evlist__set_maps(evlist, cpus, threads);
out:
        return err;
out_put:
        cpu_map__put(cpus);
        goto out;
}

int perf_evlist__open(struct perf_evlist *evlist)
{
        struct perf_evsel *evsel;
        int err;

        /*
         * Default: one fd per CPU, all threads, aka systemwide
         * as sys_perf_event_open(cpu = -1, thread = -1) is EINVAL
         */
        if (evlist->threads == NULL && evlist->cpus == NULL) {
                err = perf_evlist__create_syswide_maps(evlist);
                if (err < 0)
                        goto out_err;
        }

        perf_evlist__update_id_pos(evlist);

        evlist__for_each_entry(evlist, evsel) {
                err = perf_evsel__open(evsel, evsel->cpus, evsel->threads);
                if (err < 0)
                        goto out_err;
        }

        return 0;
out_err:
        perf_evlist__close(evlist);
        errno = -err;
        return err;
}

int perf_evlist__prepare_workload(struct perf_evlist *evlist, struct target *target,
                                  const char *argv[], bool pipe_output,
                                  void (*exec_error)(int signo, siginfo_t *info, void *ucontext))
{
        int child_ready_pipe[2], go_pipe[2];
        char bf;

        if (pipe(child_ready_pipe) < 0) {
                perror("failed to create 'ready' pipe");
                return -1;
        }

        if (pipe(go_pipe) < 0) {
                perror("failed to create 'go' pipe");
                goto out_close_ready_pipe;
        }

        evlist->workload.pid = fork();
        if (evlist->workload.pid < 0) {
                perror("failed to fork");
                goto out_close_pipes;
        }

        if (!evlist->workload.pid) {
                int ret;

                if (pipe_output)
                        dup2(2, 1);

                signal(SIGTERM, SIG_DFL);

                close(child_ready_pipe[0]);
                close(go_pipe[1]);
                fcntl(go_pipe[0], F_SETFD, FD_CLOEXEC);

                /*
                 * Tell the parent we're ready to go
                 */
                close(child_ready_pipe[1]);

                /*
                 * Wait until the parent tells us to go.
                 */
                ret = read(go_pipe[0], &bf, 1);
                /*
                 * The parent will ask for the execvp() to be performed by
                 * writing exactly one byte, in workload.cork_fd, usually via
                 * perf_evlist__start_workload().
                 *
                 * For cancelling the workload without actually running it,
                 * the parent will just close workload.cork_fd, without writing
                 * anything, i.e. read will return zero and we just exit()
                 * here.
                 */
                if (ret != 1) {
                        if (ret == -1)
                                perror("unable to read pipe");
                        exit(ret);
                }

                execvp(argv[0], (char **)argv);

                if (exec_error) {
                        union sigval val;

                        val.sival_int = errno;
                        if (sigqueue(getppid(), SIGUSR1, val))
                                perror(argv[0]);
                } else
                        perror(argv[0]);
                exit(-1);
        }

        if (exec_error) {
                struct sigaction act = {
                        .sa_flags     = SA_SIGINFO,
                        .sa_sigaction = exec_error,
                };
                sigaction(SIGUSR1, &act, NULL);
        }

        if (target__none(target)) {
                if (evlist->threads == NULL) {
                        fprintf(stderr, "FATAL: evlist->threads need to be set at this point (%s:%d).\n",
                                __func__, __LINE__);
                        goto out_close_pipes;
                }
                thread_map__set_pid(evlist->threads, 0, evlist->workload.pid);
        }

        close(child_ready_pipe[1]);
        close(go_pipe[0]);
        /*
         * wait for child to settle
         */
        if (read(child_ready_pipe[0], &bf, 1) == -1) {
                perror("unable to read pipe");
                goto out_close_pipes;
        }

        fcntl(go_pipe[1], F_SETFD, FD_CLOEXEC);
        evlist->workload.cork_fd = go_pipe[1];
        close(child_ready_pipe[0]);
        return 0;

out_close_pipes:
        close(go_pipe[0]);
        close(go_pipe[1]);
out_close_ready_pipe:
        close(child_ready_pipe[0]);
        close(child_ready_pipe[1]);
        return -1;
}

int perf_evlist__start_workload(struct perf_evlist *evlist)
{
        if (evlist->workload.cork_fd > 0) {
                char bf = 0;
                int ret;
                /*
                 * Remove the cork, let it rip!
                 */
                ret = write(evlist->workload.cork_fd, &bf, 1);
                if (ret < 0)
                        perror("enable to write to pipe");

                close(evlist->workload.cork_fd);
                return ret;
        }

        return 0;
}

int perf_evlist__parse_sample(struct perf_evlist *evlist, union perf_event *event,
                              struct perf_sample *sample)
{
        struct perf_evsel *evsel = perf_evlist__event2evsel(evlist, event);

        if (!evsel)
                return -EFAULT;
        return perf_evsel__parse_sample(evsel, event, sample);
}

size_t perf_evlist__fprintf(struct perf_evlist *evlist, FILE *fp)
{
        struct perf_evsel *evsel;
        size_t printed = 0;

        evlist__for_each_entry(evlist, evsel) {
                printed += fprintf(fp, "%s%s", evsel->idx ? ", " : "",
                                   perf_evsel__name(evsel));
        }

        return printed + fprintf(fp, "\n");
}

int perf_evlist__strerror_open(struct perf_evlist *evlist,
                               int err, char *buf, size_t size)
{
        int printed, value;
        char sbuf[STRERR_BUFSIZE], *emsg = str_error_r(err, sbuf, sizeof(sbuf));

        switch (err) {
        case EACCES:
        case EPERM:
                printed = scnprintf(buf, size,
                                    "Error:\t%s.\n"
                                    "Hint:\tCheck /proc/sys/kernel/perf_event_paranoid setting.", emsg);

                value = perf_event_paranoid();

                printed += scnprintf(buf + printed, size - printed, "\nHint:\t");

                if (value >= 2) {
                        printed += scnprintf(buf + printed, size - printed,
                                             "For your workloads it needs to be <= 1\nHint:\t");
                }
                printed += scnprintf(buf + printed, size - printed,
                                     "For system wide tracing it needs to be set to -1.\n");

                printed += scnprintf(buf + printed, size - printed,
                                    "Hint:\tTry: 'sudo sh -c \"echo -1 > /proc/sys/kernel/perf_event_paranoid\"'\n"
                                    "Hint:\tThe current value is %d.", value);
                break;
        case EINVAL: {
                struct perf_evsel *first = perf_evlist__first(evlist);
                int max_freq;

                if (sysctl__read_int("kernel/perf_event_max_sample_rate", &max_freq) < 0)
                        goto out_default;

                if (first->attr.sample_freq < (u64)max_freq)
                        goto out_default;

                printed = scnprintf(buf, size,
                                    "Error:\t%s.\n"
                                    "Hint:\tCheck /proc/sys/kernel/perf_event_max_sample_rate.\n"
                                    "Hint:\tThe current value is %d and %" PRIu64 " is being requested.",
                                    emsg, max_freq, first->attr.sample_freq);
                break;
        }
        default:
out_default:
                scnprintf(buf, size, "%s", emsg);
                break;
        }

        return 0;
}

int perf_evlist__strerror_mmap(struct perf_evlist *evlist, int err, char *buf, size_t size)
{
        char sbuf[STRERR_BUFSIZE], *emsg = str_error_r(err, sbuf, sizeof(sbuf));
        int pages_attempted = evlist->mmap_len / 1024, pages_max_per_user, printed = 0;

        switch (err) {
        case EPERM:
                sysctl__read_int("kernel/perf_event_mlock_kb", &pages_max_per_user);
                printed += scnprintf(buf + printed, size - printed,
                                     "Error:\t%s.\n"
                                     "Hint:\tCheck /proc/sys/kernel/perf_event_mlock_kb (%d kB) setting.\n"
                                     "Hint:\tTried using %zd kB.\n",
                                     emsg, pages_max_per_user, pages_attempted);

                if (pages_attempted >= pages_max_per_user) {
                        printed += scnprintf(buf + printed, size - printed,
                                             "Hint:\tTry 'sudo sh -c \"echo %d > /proc/sys/kernel/perf_event_mlock_kb\"', or\n",
                                             pages_max_per_user + pages_attempted);
                }

                printed += scnprintf(buf + printed, size - printed,
                                     "Hint:\tTry using a smaller -m/--mmap-pages value.");
                break;
        default:
                scnprintf(buf, size, "%s", emsg);
                break;
        }

        return 0;
}

void perf_evlist__to_front(struct perf_evlist *evlist,
                           struct perf_evsel *move_evsel)
{
        struct perf_evsel *evsel, *n;
        LIST_HEAD(move);

        if (move_evsel == perf_evlist__first(evlist))
                return;

        evlist__for_each_entry_safe(evlist, n, evsel) {
                if (evsel->leader == move_evsel->leader)
                        list_move_tail(&evsel->node, &move);
        }

        list_splice(&move, &evlist->entries);
}

void perf_evlist__set_tracking_event(struct perf_evlist *evlist,
                                     struct perf_evsel *tracking_evsel)
{
        struct perf_evsel *evsel;

        if (tracking_evsel->tracking)
                return;

        evlist__for_each_entry(evlist, evsel) {
                if (evsel != tracking_evsel)
                        evsel->tracking = false;
        }

        tracking_evsel->tracking = true;
}

struct perf_evsel *
perf_evlist__find_evsel_by_str(struct perf_evlist *evlist,
                               const char *str)
{
        struct perf_evsel *evsel;

        evlist__for_each_entry(evlist, evsel) {
                if (!evsel->name)
                        continue;
                if (strcmp(str, evsel->name) == 0)
                        return evsel;
        }

        return NULL;
}

void perf_evlist__toggle_bkw_mmap(struct perf_evlist *evlist,
                                  enum bkw_mmap_state state)
{
        enum bkw_mmap_state old_state = evlist->bkw_mmap_state;
        enum action {
                NONE,
                PAUSE,
                RESUME,
        } action = NONE;

        if (!evlist->backward_mmap)
                return;

        switch (old_state) {
        case BKW_MMAP_NOTREADY: {
                if (state != BKW_MMAP_RUNNING)
                        goto state_err;;
                break;
        }
        case BKW_MMAP_RUNNING: {
                if (state != BKW_MMAP_DATA_PENDING)
                        goto state_err;
                action = PAUSE;
                break;
        }
        case BKW_MMAP_DATA_PENDING: {
                if (state != BKW_MMAP_EMPTY)
                        goto state_err;
                break;
        }
        case BKW_MMAP_EMPTY: {
                if (state != BKW_MMAP_RUNNING)
                        goto state_err;
                action = RESUME;
                break;
        }
        default:
                WARN_ONCE(1, "Shouldn't get there\n");
        }

        evlist->bkw_mmap_state = state;

        switch (action) {
        case PAUSE:
                perf_evlist__pause(evlist);
                break;
        case RESUME:
                perf_evlist__resume(evlist);
                break;
        case NONE:
        default:
                break;
        }

state_err:
        return;
}