Merge tag 'perf-core-for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git...

[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 "debugfs.h"
#include <poll.h>
#include "cpumap.h"
#include "thread_map.h"
#include "evlist.h"
#include "evsel.h"
#include <unistd.h>

#include "parse-events.h"

#include <sys/mman.h>

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

#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);
        evlist->workload.pid = -1;
}

struct perf_evlist *perf_evlist__new(struct cpu_map *cpus,
                                     struct thread_map *threads)
{
        struct perf_evlist *evlist = zalloc(sizeof(*evlist));

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

        return evlist;
}

void perf_evlist__config_attrs(struct perf_evlist *evlist,
                               struct perf_record_opts *opts)
{
        struct perf_evsel *evsel;

        if (evlist->cpus->map[0] < 0)
                opts->no_inherit = true;

        list_for_each_entry(evsel, &evlist->entries, node) {
                perf_evsel__config(evsel, opts);

                if (evlist->nr_entries > 1)
                        evsel->attr.sample_type |= PERF_SAMPLE_ID;
        }
}

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

        list_for_each_entry_safe(pos, n, &evlist->entries, node) {
                list_del_init(&pos->node);
                perf_evsel__delete(pos);
        }

        evlist->nr_entries = 0;
}

void perf_evlist__exit(struct perf_evlist *evlist)
{
        free(evlist->mmap);
        free(evlist->pollfd);
        evlist->mmap = NULL;
        evlist->pollfd = NULL;
}

void perf_evlist__delete(struct perf_evlist *evlist)
{
        perf_evlist__purge(evlist);
        perf_evlist__exit(evlist);
        free(evlist);
}

void perf_evlist__add(struct perf_evlist *evlist, struct perf_evsel *entry)
{
        list_add_tail(&entry->node, &evlist->entries);
        ++evlist->nr_entries;
}

static void perf_evlist__splice_list_tail(struct perf_evlist *evlist,
                                          struct list_head *list,
                                          int nr_entries)
{
        list_splice_tail(list, &evlist->entries);
        evlist->nr_entries += nr_entries;
}

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);

        evsel = perf_evsel__new(&attr, 0);
        if (evsel == NULL)
                goto error;

        /* use strdup() because free(evsel) assumes name is allocated */
        evsel->name = strdup("cycles");
        if (!evsel->name)
                goto error_free;

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

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(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, nr_attrs);

        return 0;

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

static int trace_event__id(const char *evname)
{
        char *filename, *colon;
        int err = -1, fd;

        if (asprintf(&filename, "%s/%s/id", tracing_events_path, evname) < 0)
                return -1;

        colon = strrchr(filename, ':');
        if (colon != NULL)
                *colon = '/';

        fd = open(filename, O_RDONLY);
        if (fd >= 0) {
                char id[16];
                if (read(fd, id, sizeof(id)) > 0)
                        err = atoi(id);
                close(fd);
        }

        free(filename);
        return err;
}

int perf_evlist__add_tracepoints(struct perf_evlist *evlist,
                                 const char *tracepoints[],
                                 size_t nr_tracepoints)
{
        int err;
        size_t i;
        struct perf_event_attr *attrs = zalloc(nr_tracepoints * sizeof(*attrs));

        if (attrs == NULL)
                return -1;

        for (i = 0; i < nr_tracepoints; i++) {
                err = trace_event__id(tracepoints[i]);

                if (err < 0)
                        goto out_free_attrs;

                attrs[i].type          = PERF_TYPE_TRACEPOINT;
                attrs[i].config        = err;
                attrs[i].sample_type   = (PERF_SAMPLE_RAW | PERF_SAMPLE_TIME |
                                          PERF_SAMPLE_CPU);
                attrs[i].sample_period = 1;
        }

        err = perf_evlist__add_attrs(evlist, attrs, nr_tracepoints);
out_free_attrs:
        free(attrs);
        return err;
}

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

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

        return NULL;
}

int perf_evlist__set_tracepoints_handlers(struct perf_evlist *evlist,
                                          const struct perf_evsel_str_handler *assocs,
                                          size_t nr_assocs)
{
        struct perf_evsel *evsel;
        int err;
        size_t i;

        for (i = 0; i < nr_assocs; i++) {
                err = trace_event__id(assocs[i].name);
                if (err < 0)
                        goto out;

                evsel = perf_evlist__find_tracepoint_by_id(evlist, err);
                if (evsel == NULL)
                        continue;

                err = -EEXIST;
                if (evsel->handler.func != NULL)
                        goto out;
                evsel->handler.func = assocs[i].handler;
        }

        err = 0;
out:
        return err;
}

void perf_evlist__disable(struct perf_evlist *evlist)
{
        int cpu, thread;
        struct perf_evsel *pos;

        for (cpu = 0; cpu < evlist->cpus->nr; cpu++) {
                list_for_each_entry(pos, &evlist->entries, node) {
                        for (thread = 0; thread < evlist->threads->nr; thread++)
                                ioctl(FD(pos, cpu, thread), PERF_EVENT_IOC_DISABLE);
                }
        }
}

void perf_evlist__enable(struct perf_evlist *evlist)
{
        int cpu, thread;
        struct perf_evsel *pos;

        for (cpu = 0; cpu < evlist->cpus->nr; cpu++) {
                list_for_each_entry(pos, &evlist->entries, node) {
                        for (thread = 0; thread < evlist->threads->nr; thread++)
                                ioctl(FD(pos, cpu, thread), PERF_EVENT_IOC_ENABLE);
                }
        }
}

static int perf_evlist__alloc_pollfd(struct perf_evlist *evlist)
{
        int nfds = evlist->cpus->nr * evlist->threads->nr * evlist->nr_entries;
        evlist->pollfd = malloc(sizeof(struct pollfd) * nfds);
        return evlist->pollfd != NULL ? 0 : -ENOMEM;
}

void perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd)
{
        fcntl(fd, F_SETFL, O_NONBLOCK);
        evlist->pollfd[evlist->nr_fds].fd = fd;
        evlist->pollfd[evlist->nr_fds].events = POLLIN;
        evlist->nr_fds++;
}

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;
}

static 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 */

        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;

        perf_evlist__id_add(evlist, evsel, cpu, thread, read_data[id_idx]);
        return 0;
}

struct perf_evsel *perf_evlist__id2evsel(struct perf_evlist *evlist, u64 id)
{
        struct hlist_head *head;
        struct hlist_node *pos;
        struct perf_sample_id *sid;
        int hash;

        if (evlist->nr_entries == 1)
                return list_entry(evlist->entries.next, struct perf_evsel, node);

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

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

union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
{
        /* XXX Move this to perf.c, making it generally available */
        unsigned int page_size = sysconf(_SC_PAGE_SIZE);
        struct perf_mmap *md = &evlist->mmap[idx];
        unsigned int head = perf_mmap__read_head(md);
        unsigned int old = md->prev;
        unsigned char *data = md->base + page_size;
        union perf_event *event = NULL;

        if (evlist->overwrite) {
                /*
                 * 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 head, we got messed up.
                 *
                 * In either case, truncate and restart at head.
                 */
                int diff = head - old;
                if (diff > md->mask / 2 || diff < 0) {
                        fprintf(stderr, "WARNING: failed to keep up with mmap data.\n");

                        /*
                         * head points to a known good entry, start there.
                         */
                        old = head;
                }
        }

        if (old != head) {
                size_t size;

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

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

                old += size;
        }

        md->prev = old;

        if (!evlist->overwrite)
                perf_mmap__write_tail(md, old);

        return event;
}

void perf_evlist__munmap(struct perf_evlist *evlist)
{
        int i;

        for (i = 0; i < evlist->nr_mmaps; i++) {
                if (evlist->mmap[i].base != NULL) {
                        munmap(evlist->mmap[i].base, evlist->mmap_len);
                        evlist->mmap[i].base = NULL;
                }
        }

        free(evlist->mmap);
        evlist->mmap = NULL;
}

static int perf_evlist__alloc_mmap(struct perf_evlist *evlist)
{
        evlist->nr_mmaps = evlist->cpus->nr;
        if (evlist->cpus->map[0] == -1)
                evlist->nr_mmaps = evlist->threads->nr;
        evlist->mmap = zalloc(evlist->nr_mmaps * sizeof(struct perf_mmap));
        return evlist->mmap != NULL ? 0 : -ENOMEM;
}

static int __perf_evlist__mmap(struct perf_evlist *evlist,
                               int idx, int prot, int mask, int fd)
{
        evlist->mmap[idx].prev = 0;
        evlist->mmap[idx].mask = mask;
        evlist->mmap[idx].base = mmap(NULL, evlist->mmap_len, prot,
                                      MAP_SHARED, fd, 0);
        if (evlist->mmap[idx].base == MAP_FAILED) {
                evlist->mmap[idx].base = NULL;
                return -1;
        }

        perf_evlist__add_pollfd(evlist, fd);
        return 0;
}

static int perf_evlist__mmap_per_cpu(struct perf_evlist *evlist, int prot, int mask)
{
        struct perf_evsel *evsel;
        int cpu, thread;

        for (cpu = 0; cpu < evlist->cpus->nr; cpu++) {
                int output = -1;

                for (thread = 0; thread < evlist->threads->nr; thread++) {
                        list_for_each_entry(evsel, &evlist->entries, node) {
                                int fd = FD(evsel, cpu, thread);

                                if (output == -1) {
                                        output = fd;
                                        if (__perf_evlist__mmap(evlist, cpu,
                                                                prot, mask, output) < 0)
                                                goto out_unmap;
                                } else {
                                        if (ioctl(fd, PERF_EVENT_IOC_SET_OUTPUT, output) != 0)
                                                goto out_unmap;
                                }

                                if ((evsel->attr.read_format & PERF_FORMAT_ID) &&
                                    perf_evlist__id_add_fd(evlist, evsel, cpu, thread, fd) < 0)
                                        goto out_unmap;
                        }
                }
        }

        return 0;

out_unmap:
        for (cpu = 0; cpu < evlist->cpus->nr; cpu++) {
                if (evlist->mmap[cpu].base != NULL) {
                        munmap(evlist->mmap[cpu].base, evlist->mmap_len);
                        evlist->mmap[cpu].base = NULL;
                }
        }
        return -1;
}

static int perf_evlist__mmap_per_thread(struct perf_evlist *evlist, int prot, int mask)
{
        struct perf_evsel *evsel;
        int thread;

        for (thread = 0; thread < evlist->threads->nr; thread++) {
                int output = -1;

                list_for_each_entry(evsel, &evlist->entries, node) {
                        int fd = FD(evsel, 0, thread);

                        if (output == -1) {
                                output = fd;
                                if (__perf_evlist__mmap(evlist, thread,
                                                        prot, mask, output) < 0)
                                        goto out_unmap;
                        } else {
                                if (ioctl(fd, PERF_EVENT_IOC_SET_OUTPUT, output) != 0)
                                        goto out_unmap;
                        }

                        if ((evsel->attr.read_format & PERF_FORMAT_ID) &&
                            perf_evlist__id_add_fd(evlist, evsel, 0, thread, fd) < 0)
                                goto out_unmap;
                }
        }

        return 0;

out_unmap:
        for (thread = 0; thread < evlist->threads->nr; thread++) {
                if (evlist->mmap[thread].base != NULL) {
                        munmap(evlist->mmap[thread].base, evlist->mmap_len);
                        evlist->mmap[thread].base = NULL;
                }
        }
        return -1;
}

/** perf_evlist__mmap - Create per cpu maps to receive events
 *
 * @evlist - list of events
 * @pages - map length in pages
 * @overwrite - overwrite older events?
 *
 * If overwrite is false the user needs to signal event consuption using:
 *
 *      struct perf_mmap *m = &evlist->mmap[cpu];
 *      unsigned int head = perf_mmap__read_head(m);
 *
 *      perf_mmap__write_tail(m, head)
 *
 * Using perf_evlist__read_on_cpu does this automatically.
 */
int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
                      bool overwrite)
{
        unsigned int page_size = sysconf(_SC_PAGE_SIZE);
        struct perf_evsel *evsel;
        const struct cpu_map *cpus = evlist->cpus;
        const struct thread_map *threads = evlist->threads;
        int prot = PROT_READ | (overwrite ? 0 : PROT_WRITE), mask;

        /* 512 kiB: default amount of unprivileged mlocked memory */
        if (pages == UINT_MAX)
                pages = (512 * 1024) / page_size;
        else if (!is_power_of_2(pages))
                return -EINVAL;

        mask = pages * page_size - 1;

        if (evlist->mmap == NULL && perf_evlist__alloc_mmap(evlist) < 0)
                return -ENOMEM;

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

        evlist->overwrite = overwrite;
        evlist->mmap_len = (pages + 1) * page_size;

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

        if (evlist->cpus->map[0] == -1)
                return perf_evlist__mmap_per_thread(evlist, prot, mask);

        return perf_evlist__mmap_per_cpu(evlist, prot, mask);
}

int perf_evlist__create_maps(struct perf_evlist *evlist, pid_t target_pid,
                             pid_t target_tid, uid_t uid, const char *cpu_list)
{
        evlist->threads = thread_map__new(target_pid, target_tid, uid);

        if (evlist->threads == NULL)
                return -1;

        if (uid != UINT_MAX || (cpu_list == NULL && target_tid != -1))
                evlist->cpus = cpu_map__dummy_new();
        else
                evlist->cpus = cpu_map__new(cpu_list);

        if (evlist->cpus == NULL)
                goto out_delete_threads;

        return 0;

out_delete_threads:
        thread_map__delete(evlist->threads);
        return -1;
}

void perf_evlist__delete_maps(struct perf_evlist *evlist)
{
        cpu_map__delete(evlist->cpus);
        thread_map__delete(evlist->threads);
        evlist->cpus    = NULL;
        evlist->threads = NULL;
}

int perf_evlist__set_filters(struct perf_evlist *evlist)
{
        const struct thread_map *threads = evlist->threads;
        const struct cpu_map *cpus = evlist->cpus;
        struct perf_evsel *evsel;
        char *filter;
        int thread;
        int cpu;
        int err;
        int fd;

        list_for_each_entry(evsel, &evlist->entries, node) {
                filter = evsel->filter;
                if (!filter)
                        continue;
                for (cpu = 0; cpu < cpus->nr; cpu++) {
                        for (thread = 0; thread < threads->nr; thread++) {
                                fd = FD(evsel, cpu, thread);
                                err = ioctl(fd, PERF_EVENT_IOC_SET_FILTER, filter);
                                if (err)
                                        return err;
                        }
                }
        }

        return 0;
}

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

        pos = first = list_entry(evlist->entries.next, struct perf_evsel, node);

        list_for_each_entry_continue(pos, &evlist->entries, node) {
                if (first->attr.sample_type != pos->attr.sample_type)
                        return false;
        }

        return true;
}

u64 perf_evlist__sample_type(const struct perf_evlist *evlist)
{
        struct perf_evsel *first;

        first = list_entry(evlist->entries.next, struct perf_evsel, node);
        return first->attr.sample_type;
}

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

        first = list_entry(evlist->entries.next, struct perf_evsel, node);

        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;
out:
        return size;
}

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

        pos = first = list_entry(evlist->entries.next, struct perf_evsel, node);

        list_for_each_entry_continue(pos, &evlist->entries, node) {
                if (first->attr.sample_id_all != pos->attr.sample_id_all)
                        return false;
        }

        return true;
}

bool perf_evlist__sample_id_all(const struct perf_evlist *evlist)
{
        struct perf_evsel *first;

        first = list_entry(evlist->entries.next, struct perf_evsel, node);
        return first->attr.sample_id_all;
}

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

int perf_evlist__open(struct perf_evlist *evlist, bool group)
{
        struct perf_evsel *evsel, *first;
        int err, ncpus, nthreads;

        first = list_entry(evlist->entries.next, struct perf_evsel, node);

        list_for_each_entry(evsel, &evlist->entries, node) {
                struct xyarray *group_fd = NULL;

                if (group && evsel != first)
                        group_fd = first->fd;

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

        return 0;
out_err:
        ncpus = evlist->cpus ? evlist->cpus->nr : 1;
        nthreads = evlist->threads ? evlist->threads->nr : 1;

        list_for_each_entry_reverse(evsel, &evlist->entries, node)
                perf_evsel__close(evsel, ncpus, nthreads);

        return err;
}

int perf_evlist__prepare_workload(struct perf_evlist *evlist,
                                  struct perf_record_opts *opts,
                                  const char *argv[])
{
        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) {
                if (opts->pipe_output)
                        dup2(2, 1);

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

                /*
                 * Do a dummy execvp to get the PLT entry resolved,
                 * so we avoid the resolver overhead on the real
                 * execvp call.
                 */
                execvp("", (char **)argv);

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

                /*
                 * Wait until the parent tells us to go.
                 */
                if (read(go_pipe[0], &bf, 1) == -1)
                        perror("unable to read pipe");

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

                perror(argv[0]);
                kill(getppid(), SIGUSR1);
                exit(-1);
        }

        if (!opts->system_wide && opts->target_tid == -1 && opts->target_pid == -1)
                evlist->threads->map[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;
        }

        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) {
                /*
                 * Remove the cork, let it rip!
                 */
                return close(evlist->workload.cork_fd);
        }

        return 0;
}