*/
#include "qemu/osdep.h"
-#include "qemu-common.h"
#include "block/block.h"
+#include "block/thread-pool.h"
+#include "qemu/main-loop.h"
+#include "qemu/rcu.h"
#include "qemu/rcu_queue.h"
#include "qemu/sockets.h"
#include "qemu/cutils.h"
#include "trace.h"
-#ifdef CONFIG_EPOLL_CREATE1
-#include <sys/epoll.h>
-#endif
+#include "aio-posix.h"
-struct AioHandler
-{
- GPollFD pfd;
- IOHandler *io_read;
- IOHandler *io_write;
- AioPollFn *io_poll;
- IOHandler *io_poll_begin;
- IOHandler *io_poll_end;
- int deleted;
- void *opaque;
- bool is_external;
- QLIST_ENTRY(AioHandler) node;
-};
-
-#ifdef CONFIG_EPOLL_CREATE1
-
-/* The fd number threshold to switch to epoll */
-#define EPOLL_ENABLE_THRESHOLD 64
-
-static void aio_epoll_disable(AioContext *ctx)
-{
- ctx->epoll_enabled = false;
- if (!ctx->epoll_available) {
- return;
- }
- ctx->epoll_available = false;
- close(ctx->epollfd);
-}
-
-static inline int epoll_events_from_pfd(int pfd_events)
-{
- return (pfd_events & G_IO_IN ? EPOLLIN : 0) |
- (pfd_events & G_IO_OUT ? EPOLLOUT : 0) |
- (pfd_events & G_IO_HUP ? EPOLLHUP : 0) |
- (pfd_events & G_IO_ERR ? EPOLLERR : 0);
-}
-
-static bool aio_epoll_try_enable(AioContext *ctx)
-{
- AioHandler *node;
- struct epoll_event event;
-
- QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
- int r;
- if (node->deleted || !node->pfd.events) {
- continue;
- }
- event.events = epoll_events_from_pfd(node->pfd.events);
- event.data.ptr = node;
- r = epoll_ctl(ctx->epollfd, EPOLL_CTL_ADD, node->pfd.fd, &event);
- if (r) {
- return false;
- }
- }
- ctx->epoll_enabled = true;
- return true;
-}
-
-static void aio_epoll_update(AioContext *ctx, AioHandler *node, bool is_new)
-{
- struct epoll_event event;
- int r;
- int ctl;
-
- if (!ctx->epoll_enabled) {
- return;
- }
- if (!node->pfd.events) {
- ctl = EPOLL_CTL_DEL;
- } else {
- event.data.ptr = node;
- event.events = epoll_events_from_pfd(node->pfd.events);
- ctl = is_new ? EPOLL_CTL_ADD : EPOLL_CTL_MOD;
- }
-
- r = epoll_ctl(ctx->epollfd, ctl, node->pfd.fd, &event);
- if (r) {
- aio_epoll_disable(ctx);
- }
-}
+/* Stop userspace polling on a handler if it isn't active for some time */
+#define POLL_IDLE_INTERVAL_NS (7 * NANOSECONDS_PER_SECOND)
-static int aio_epoll(AioContext *ctx, GPollFD *pfds,
- unsigned npfd, int64_t timeout)
+bool aio_poll_disabled(AioContext *ctx)
{
- AioHandler *node;
- int i, ret = 0;
- struct epoll_event events[128];
-
- assert(npfd == 1);
- assert(pfds[0].fd == ctx->epollfd);
- if (timeout > 0) {
- ret = qemu_poll_ns(pfds, npfd, timeout);
- }
- if (timeout <= 0 || ret > 0) {
- ret = epoll_wait(ctx->epollfd, events,
- ARRAY_SIZE(events),
- timeout);
- if (ret <= 0) {
- goto out;
- }
- for (i = 0; i < ret; i++) {
- int ev = events[i].events;
- node = events[i].data.ptr;
- node->pfd.revents = (ev & EPOLLIN ? G_IO_IN : 0) |
- (ev & EPOLLOUT ? G_IO_OUT : 0) |
- (ev & EPOLLHUP ? G_IO_HUP : 0) |
- (ev & EPOLLERR ? G_IO_ERR : 0);
- }
- }
-out:
- return ret;
+ return qatomic_read(&ctx->poll_disable_cnt);
}
-static bool aio_epoll_enabled(AioContext *ctx)
+void aio_add_ready_handler(AioHandlerList *ready_list,
+ AioHandler *node,
+ int revents)
{
- /* Fall back to ppoll when external clients are disabled. */
- return !aio_external_disabled(ctx) && ctx->epoll_enabled;
+ QLIST_SAFE_REMOVE(node, node_ready); /* remove from nested parent's list */
+ node->pfd.revents = revents;
+ QLIST_INSERT_HEAD(ready_list, node, node_ready);
}
-static bool aio_epoll_check_poll(AioContext *ctx, GPollFD *pfds,
- unsigned npfd, int64_t timeout)
+static void aio_add_poll_ready_handler(AioHandlerList *ready_list,
+ AioHandler *node)
{
- if (!ctx->epoll_available) {
- return false;
- }
- if (aio_epoll_enabled(ctx)) {
- return true;
- }
- if (npfd >= EPOLL_ENABLE_THRESHOLD) {
- if (aio_epoll_try_enable(ctx)) {
- return true;
- } else {
- aio_epoll_disable(ctx);
- }
- }
- return false;
+ QLIST_SAFE_REMOVE(node, node_ready); /* remove from nested parent's list */
+ node->poll_ready = true;
+ QLIST_INSERT_HEAD(ready_list, node, node_ready);
}
-#else
-
-static void aio_epoll_update(AioContext *ctx, AioHandler *node, bool is_new)
-{
-}
-
-static int aio_epoll(AioContext *ctx, GPollFD *pfds,
- unsigned npfd, int64_t timeout)
-{
- assert(false);
-}
-
-static bool aio_epoll_enabled(AioContext *ctx)
-{
- return false;
-}
-
-static bool aio_epoll_check_poll(AioContext *ctx, GPollFD *pfds,
- unsigned npfd, int64_t timeout)
-{
- return false;
-}
-
-#endif
-
static AioHandler *find_aio_handler(AioContext *ctx, int fd)
{
AioHandler *node;
QLIST_FOREACH(node, &ctx->aio_handlers, node) {
- if (node->pfd.fd == fd)
- if (!node->deleted)
+ if (node->pfd.fd == fd) {
+ if (!QLIST_IS_INSERTED(node, node_deleted)) {
return node;
+ }
+ }
}
return NULL;
g_source_remove_poll(&ctx->source, &node->pfd);
}
+ node->pfd.revents = 0;
+ node->poll_ready = false;
+
+ /* If the fd monitor has already marked it deleted, leave it alone */
+ if (QLIST_IS_INSERTED(node, node_deleted)) {
+ return false;
+ }
+
/* If a read is in progress, just mark the node as deleted */
if (qemu_lockcnt_count(&ctx->list_lock)) {
- node->deleted = 1;
- node->pfd.revents = 0;
+ QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted);
return false;
}
/* Otherwise, delete it for real. We can't just mark it as
* deleted because deleted nodes are only cleaned up while
* no one is walking the handlers list.
*/
+ QLIST_SAFE_REMOVE(node, node_poll);
QLIST_REMOVE(node, node);
return true;
}
void aio_set_fd_handler(AioContext *ctx,
int fd,
- bool is_external,
IOHandler *io_read,
IOHandler *io_write,
AioPollFn *io_poll,
+ IOHandler *io_poll_ready,
void *opaque)
{
AioHandler *node;
bool deleted = false;
int poll_disable_change;
+ if (io_poll && !io_poll_ready) {
+ io_poll = NULL; /* polling only makes sense if there is a handler */
+ }
+
qemu_lockcnt_lock(&ctx->list_lock);
node = find_aio_handler(ctx, fd);
new_node->io_read = io_read;
new_node->io_write = io_write;
new_node->io_poll = io_poll;
+ new_node->io_poll_ready = io_poll_ready;
new_node->opaque = opaque;
- new_node->is_external = is_external;
if (is_new) {
new_node->pfd.fd = fd;
QLIST_INSERT_HEAD_RCU(&ctx->aio_handlers, new_node, node);
}
- if (node) {
- deleted = aio_remove_fd_handler(ctx, node);
- }
/* No need to order poll_disable_cnt writes against other updates;
* the counter is only used to avoid wasting time and latency on
* Changing handlers is a rare event, and a little wasted polling until
* the aio_notify below is not an issue.
*/
- atomic_set(&ctx->poll_disable_cnt,
- atomic_read(&ctx->poll_disable_cnt) + poll_disable_change);
+ qatomic_set(&ctx->poll_disable_cnt,
+ qatomic_read(&ctx->poll_disable_cnt) + poll_disable_change);
- if (new_node) {
- aio_epoll_update(ctx, new_node, is_new);
- } else if (node) {
- /* Unregister deleted fd_handler */
- aio_epoll_update(ctx, node, false);
+ ctx->fdmon_ops->update(ctx, node, new_node);
+ if (node) {
+ deleted = aio_remove_fd_handler(ctx, node);
}
qemu_lockcnt_unlock(&ctx->list_lock);
aio_notify(ctx);
}
}
-void aio_set_fd_poll(AioContext *ctx, int fd,
- IOHandler *io_poll_begin,
- IOHandler *io_poll_end)
+static void aio_set_fd_poll(AioContext *ctx, int fd,
+ IOHandler *io_poll_begin,
+ IOHandler *io_poll_end)
{
AioHandler *node = find_aio_handler(ctx, fd);
void aio_set_event_notifier(AioContext *ctx,
EventNotifier *notifier,
- bool is_external,
EventNotifierHandler *io_read,
- AioPollFn *io_poll)
+ AioPollFn *io_poll,
+ EventNotifierHandler *io_poll_ready)
{
- aio_set_fd_handler(ctx, event_notifier_get_fd(notifier), is_external,
- (IOHandler *)io_read, NULL, io_poll, notifier);
+ aio_set_fd_handler(ctx, event_notifier_get_fd(notifier),
+ (IOHandler *)io_read, NULL, io_poll,
+ (IOHandler *)io_poll_ready, notifier);
}
void aio_set_event_notifier_poll(AioContext *ctx,
(IOHandler *)io_poll_end);
}
-static void poll_set_started(AioContext *ctx, bool started)
+static bool poll_set_started(AioContext *ctx, AioHandlerList *ready_list,
+ bool started)
{
AioHandler *node;
+ bool progress = false;
if (started == ctx->poll_started) {
- return;
+ return false;
}
ctx->poll_started = started;
qemu_lockcnt_inc(&ctx->list_lock);
- QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
+ QLIST_FOREACH(node, &ctx->poll_aio_handlers, node_poll) {
IOHandler *fn;
- if (node->deleted) {
+ if (QLIST_IS_INSERTED(node, node_deleted)) {
continue;
}
if (fn) {
fn(node->opaque);
}
+
+ /* Poll one last time in case ->io_poll_end() raced with the event */
+ if (!started && node->io_poll(node->opaque)) {
+ aio_add_poll_ready_handler(ready_list, node);
+ progress = true;
+ }
}
qemu_lockcnt_dec(&ctx->list_lock);
+
+ return progress;
}
bool aio_prepare(AioContext *ctx)
{
+ AioHandlerList ready_list = QLIST_HEAD_INITIALIZER(ready_list);
+
/* Poll mode cannot be used with glib's event loop, disable it. */
- poll_set_started(ctx, false);
+ poll_set_started(ctx, &ready_list, false);
+ /* TODO what to do with this list? */
return false;
}
QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
int revents;
+ /* TODO should this check poll ready? */
revents = node->pfd.revents & node->pfd.events;
- if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read &&
- aio_node_check(ctx, node->is_external)) {
+ if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read) {
result = true;
break;
}
- if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write &&
- aio_node_check(ctx, node->is_external)) {
+ if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write) {
result = true;
break;
}
return result;
}
-static bool aio_dispatch_handlers(AioContext *ctx)
+static void aio_free_deleted_handlers(AioContext *ctx)
+{
+ AioHandler *node;
+
+ if (QLIST_EMPTY_RCU(&ctx->deleted_aio_handlers)) {
+ return;
+ }
+ if (!qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {
+ return; /* we are nested, let the parent do the freeing */
+ }
+
+ while ((node = QLIST_FIRST_RCU(&ctx->deleted_aio_handlers))) {
+ QLIST_REMOVE(node, node);
+ QLIST_REMOVE(node, node_deleted);
+ QLIST_SAFE_REMOVE(node, node_poll);
+ g_free(node);
+ }
+
+ qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
+}
+
+static bool aio_dispatch_handler(AioContext *ctx, AioHandler *node)
{
- AioHandler *node, *tmp;
bool progress = false;
+ bool poll_ready;
+ int revents;
- QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) {
- int revents;
+ revents = node->pfd.revents & node->pfd.events;
+ node->pfd.revents = 0;
- revents = node->pfd.revents & node->pfd.events;
- node->pfd.revents = 0;
+ poll_ready = node->poll_ready;
+ node->poll_ready = false;
+
+ /*
+ * Start polling AioHandlers when they become ready because activity is
+ * likely to continue. Note that starvation is theoretically possible when
+ * fdmon_supports_polling(), but only until the fd fires for the first
+ * time.
+ */
+ if (!QLIST_IS_INSERTED(node, node_deleted) &&
+ !QLIST_IS_INSERTED(node, node_poll) &&
+ node->io_poll) {
+ trace_poll_add(ctx, node, node->pfd.fd, revents);
+ if (ctx->poll_started && node->io_poll_begin) {
+ node->io_poll_begin(node->opaque);
+ }
+ QLIST_INSERT_HEAD(&ctx->poll_aio_handlers, node, node_poll);
+ }
+ if (!QLIST_IS_INSERTED(node, node_deleted) &&
+ poll_ready && revents == 0 && node->io_poll_ready) {
+ /*
+ * Remove temporarily to avoid infinite loops when ->io_poll_ready()
+ * calls aio_poll() before clearing the condition that made the poll
+ * handler become ready.
+ */
+ QLIST_SAFE_REMOVE(node, node_poll);
- if (!node->deleted &&
- (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) &&
- aio_node_check(ctx, node->is_external) &&
- node->io_read) {
- node->io_read(node->opaque);
+ node->io_poll_ready(node->opaque);
- /* aio_notify() does not count as progress */
- if (node->opaque != &ctx->notifier) {
- progress = true;
- }
+ if (!QLIST_IS_INSERTED(node, node_poll)) {
+ QLIST_INSERT_HEAD(&ctx->poll_aio_handlers, node, node_poll);
}
- if (!node->deleted &&
- (revents & (G_IO_OUT | G_IO_ERR)) &&
- aio_node_check(ctx, node->is_external) &&
- node->io_write) {
- node->io_write(node->opaque);
+
+ /*
+ * Return early since revents was zero. aio_notify() does not count as
+ * progress.
+ */
+ return node->opaque != &ctx->notifier;
+ }
+
+ if (!QLIST_IS_INSERTED(node, node_deleted) &&
+ (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) &&
+ node->io_read) {
+ node->io_read(node->opaque);
+
+ /* aio_notify() does not count as progress */
+ if (node->opaque != &ctx->notifier) {
progress = true;
}
+ }
+ if (!QLIST_IS_INSERTED(node, node_deleted) &&
+ (revents & (G_IO_OUT | G_IO_ERR)) &&
+ node->io_write) {
+ node->io_write(node->opaque);
+ progress = true;
+ }
- if (node->deleted) {
- if (qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {
- QLIST_REMOVE(node, node);
- g_free(node);
- qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
- }
- }
+ return progress;
+}
+
+/*
+ * If we have a list of ready handlers then this is more efficient than
+ * scanning all handlers with aio_dispatch_handlers().
+ */
+static bool aio_dispatch_ready_handlers(AioContext *ctx,
+ AioHandlerList *ready_list)
+{
+ bool progress = false;
+ AioHandler *node;
+
+ while ((node = QLIST_FIRST(ready_list))) {
+ QLIST_REMOVE(node, node_ready);
+ progress = aio_dispatch_handler(ctx, node) || progress;
+ }
+
+ return progress;
+}
+
+/* Slower than aio_dispatch_ready_handlers() but only used via glib */
+static bool aio_dispatch_handlers(AioContext *ctx)
+{
+ AioHandler *node, *tmp;
+ bool progress = false;
+
+ QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) {
+ progress = aio_dispatch_handler(ctx, node) || progress;
}
return progress;
qemu_lockcnt_inc(&ctx->list_lock);
aio_bh_poll(ctx);
aio_dispatch_handlers(ctx);
+ aio_free_deleted_handlers(ctx);
qemu_lockcnt_dec(&ctx->list_lock);
timerlistgroup_run_timers(&ctx->tlg);
}
-/* These thread-local variables are used only in a small part of aio_poll
- * around the call to the poll() system call. In particular they are not
- * used while aio_poll is performing callbacks, which makes it much easier
- * to think about reentrancy!
- *
- * Stack-allocated arrays would be perfect but they have size limitations;
- * heap allocation is expensive enough that we want to reuse arrays across
- * calls to aio_poll(). And because poll() has to be called without holding
- * any lock, the arrays cannot be stored in AioContext. Thread-local data
- * has none of the disadvantages of these three options.
- */
-static __thread GPollFD *pollfds;
-static __thread AioHandler **nodes;
-static __thread unsigned npfd, nalloc;
-static __thread Notifier pollfds_cleanup_notifier;
-
-static void pollfds_cleanup(Notifier *n, void *unused)
-{
- g_assert(npfd == 0);
- g_free(pollfds);
- g_free(nodes);
- nalloc = 0;
-}
-
-static void add_pollfd(AioHandler *node)
-{
- if (npfd == nalloc) {
- if (nalloc == 0) {
- pollfds_cleanup_notifier.notify = pollfds_cleanup;
- qemu_thread_atexit_add(&pollfds_cleanup_notifier);
- nalloc = 8;
- } else {
- g_assert(nalloc <= INT_MAX);
- nalloc *= 2;
- }
- pollfds = g_renew(GPollFD, pollfds, nalloc);
- nodes = g_renew(AioHandler *, nodes, nalloc);
- }
- nodes[npfd] = node;
- pollfds[npfd] = (GPollFD) {
- .fd = node->pfd.fd,
- .events = node->pfd.events,
- };
- npfd++;
-}
-
-static bool run_poll_handlers_once(AioContext *ctx, int64_t *timeout)
+static bool run_poll_handlers_once(AioContext *ctx,
+ AioHandlerList *ready_list,
+ int64_t now,
+ int64_t *timeout)
{
bool progress = false;
AioHandler *node;
+ AioHandler *tmp;
+
+ QLIST_FOREACH_SAFE(node, &ctx->poll_aio_handlers, node_poll, tmp) {
+ if (node->io_poll(node->opaque)) {
+ aio_add_poll_ready_handler(ready_list, node);
+
+ node->poll_idle_timeout = now + POLL_IDLE_INTERVAL_NS;
- QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
- if (!node->deleted && node->io_poll &&
- aio_node_check(ctx, node->is_external) &&
- node->io_poll(node->opaque)) {
/*
* Polling was successful, exit try_poll_mode immediately
* to adjust the next polling time.
return progress;
}
+static bool fdmon_supports_polling(AioContext *ctx)
+{
+ return ctx->fdmon_ops->need_wait != aio_poll_disabled;
+}
+
+static bool remove_idle_poll_handlers(AioContext *ctx,
+ AioHandlerList *ready_list,
+ int64_t now)
+{
+ AioHandler *node;
+ AioHandler *tmp;
+ bool progress = false;
+
+ /*
+ * File descriptor monitoring implementations without userspace polling
+ * support suffer from starvation when a subset of handlers is polled
+ * because fds will not be processed in a timely fashion. Don't remove
+ * idle poll handlers.
+ */
+ if (!fdmon_supports_polling(ctx)) {
+ return false;
+ }
+
+ QLIST_FOREACH_SAFE(node, &ctx->poll_aio_handlers, node_poll, tmp) {
+ if (node->poll_idle_timeout == 0LL) {
+ node->poll_idle_timeout = now + POLL_IDLE_INTERVAL_NS;
+ } else if (now >= node->poll_idle_timeout) {
+ trace_poll_remove(ctx, node, node->pfd.fd);
+ node->poll_idle_timeout = 0LL;
+ QLIST_SAFE_REMOVE(node, node_poll);
+ if (ctx->poll_started && node->io_poll_end) {
+ node->io_poll_end(node->opaque);
+
+ /*
+ * Final poll in case ->io_poll_end() races with an event.
+ * Nevermind about re-adding the handler in the rare case where
+ * this causes progress.
+ */
+ if (node->io_poll(node->opaque)) {
+ aio_add_poll_ready_handler(ready_list, node);
+ progress = true;
+ }
+ }
+ }
+ }
+
+ return progress;
+}
+
/* run_poll_handlers:
* @ctx: the AioContext
+ * @ready_list: the list to place ready handlers on
* @max_ns: maximum time to poll for, in nanoseconds
*
* Polls for a given time.
*
- * Note that ctx->notify_me must be non-zero so this function can detect
- * aio_notify().
- *
* Note that the caller must have incremented ctx->list_lock.
*
* Returns: true if progress was made, false otherwise
*/
-static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout)
+static bool run_poll_handlers(AioContext *ctx, AioHandlerList *ready_list,
+ int64_t max_ns, int64_t *timeout)
{
bool progress;
int64_t start_time, elapsed_time;
- assert(ctx->notify_me);
assert(qemu_lockcnt_count(&ctx->list_lock) > 0);
trace_run_poll_handlers_begin(ctx, max_ns, *timeout);
+ /*
+ * Optimization: ->io_poll() handlers often contain RCU read critical
+ * sections and we therefore see many rcu_read_lock() -> rcu_read_unlock()
+ * -> rcu_read_lock() -> ... sequences with expensive memory
+ * synchronization primitives. Make the entire polling loop an RCU
+ * critical section because nested rcu_read_lock()/rcu_read_unlock() calls
+ * are cheap.
+ */
+ RCU_READ_LOCK_GUARD();
+
start_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
do {
- progress = run_poll_handlers_once(ctx, timeout);
+ progress = run_poll_handlers_once(ctx, ready_list,
+ start_time, timeout);
elapsed_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start_time;
max_ns = qemu_soonest_timeout(*timeout, max_ns);
assert(!(max_ns && progress));
- } while (elapsed_time < max_ns && !atomic_read(&ctx->poll_disable_cnt));
+ } while (elapsed_time < max_ns && !ctx->fdmon_ops->need_wait(ctx));
+
+ if (remove_idle_poll_handlers(ctx, ready_list,
+ start_time + elapsed_time)) {
+ *timeout = 0;
+ progress = true;
+ }
/* If time has passed with no successful polling, adjust *timeout to
* keep the same ending time.
/* try_poll_mode:
* @ctx: the AioContext
+ * @ready_list: list to add handlers that need to be run
* @timeout: timeout for blocking wait, computed by the caller and updated if
* polling succeeds.
*
- * ctx->notify_me must be non-zero so this function can detect aio_notify().
- *
* Note that the caller must have incremented ctx->list_lock.
*
* Returns: true if progress was made, false otherwise
*/
-static bool try_poll_mode(AioContext *ctx, int64_t *timeout)
+static bool try_poll_mode(AioContext *ctx, AioHandlerList *ready_list,
+ int64_t *timeout)
{
- int64_t max_ns = qemu_soonest_timeout(*timeout, ctx->poll_ns);
+ int64_t max_ns;
+
+ if (QLIST_EMPTY_RCU(&ctx->poll_aio_handlers)) {
+ return false;
+ }
- if (max_ns && !atomic_read(&ctx->poll_disable_cnt)) {
- poll_set_started(ctx, true);
+ max_ns = qemu_soonest_timeout(*timeout, ctx->poll_ns);
+ if (max_ns && !ctx->fdmon_ops->need_wait(ctx)) {
+ /*
+ * Enable poll mode. It pairs with the poll_set_started() in
+ * aio_poll() which disables poll mode.
+ */
+ poll_set_started(ctx, ready_list, true);
- if (run_poll_handlers(ctx, max_ns, timeout)) {
+ if (run_poll_handlers(ctx, ready_list, max_ns, timeout)) {
return true;
}
}
-
- poll_set_started(ctx, false);
-
- /* Even if we don't run busy polling, try polling once in case it can make
- * progress and the caller will be able to avoid ppoll(2)/epoll_wait(2).
- */
- return run_poll_handlers_once(ctx, timeout);
+ return false;
}
bool aio_poll(AioContext *ctx, bool blocking)
{
- AioHandler *node;
- int i;
- int ret = 0;
+ AioHandlerList ready_list = QLIST_HEAD_INITIALIZER(ready_list);
bool progress;
+ bool use_notify_me;
int64_t timeout;
int64_t start = 0;
- assert(in_aio_context_home_thread(ctx));
-
- /* aio_notify can avoid the expensive event_notifier_set if
- * everything (file descriptors, bottom halves, timers) will
- * be re-evaluated before the next blocking poll(). This is
- * already true when aio_poll is called with blocking == false;
- * if blocking == true, it is only true after poll() returns,
- * so disable the optimization now.
+ /*
+ * There cannot be two concurrent aio_poll calls for the same AioContext (or
+ * an aio_poll concurrent with a GSource prepare/check/dispatch callback).
+ * We rely on this below to avoid slow locked accesses to ctx->notify_me.
+ *
+ * aio_poll() may only be called in the AioContext's thread. iohandler_ctx
+ * is special in that it runs in the main thread, but that thread's context
+ * is qemu_aio_context.
*/
- if (blocking) {
- atomic_add(&ctx->notify_me, 2);
- }
+ assert(in_aio_context_home_thread(ctx == iohandler_get_aio_context() ?
+ qemu_get_aio_context() : ctx));
qemu_lockcnt_inc(&ctx->list_lock);
}
timeout = blocking ? aio_compute_timeout(ctx) : 0;
- progress = try_poll_mode(ctx, &timeout);
+ progress = try_poll_mode(ctx, &ready_list, &timeout);
assert(!(timeout && progress));
+ /*
+ * aio_notify can avoid the expensive event_notifier_set if
+ * everything (file descriptors, bottom halves, timers) will
+ * be re-evaluated before the next blocking poll(). This is
+ * already true when aio_poll is called with blocking == false;
+ * if blocking == true, it is only true after poll() returns,
+ * so disable the optimization now.
+ */
+ use_notify_me = timeout != 0;
+ if (use_notify_me) {
+ qatomic_set(&ctx->notify_me, qatomic_read(&ctx->notify_me) + 2);
+ /*
+ * Write ctx->notify_me before reading ctx->notified. Pairs with
+ * smp_mb in aio_notify().
+ */
+ smp_mb();
+
+ /* Don't block if aio_notify() was called */
+ if (qatomic_read(&ctx->notified)) {
+ timeout = 0;
+ }
+ }
+
/* If polling is allowed, non-blocking aio_poll does not need the
* system call---a single round of run_poll_handlers_once suffices.
*/
- if (timeout || atomic_read(&ctx->poll_disable_cnt)) {
- assert(npfd == 0);
-
- /* fill pollfds */
-
- if (!aio_epoll_enabled(ctx)) {
- QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
- if (!node->deleted && node->pfd.events
- && aio_node_check(ctx, node->is_external)) {
- add_pollfd(node);
- }
- }
+ if (timeout || ctx->fdmon_ops->need_wait(ctx)) {
+ /*
+ * Disable poll mode. poll mode should be disabled before the call
+ * of ctx->fdmon_ops->wait() so that guest's notification can wake
+ * up IO threads when some work becomes pending. It is essential to
+ * avoid hangs or unnecessary latency.
+ */
+ if (poll_set_started(ctx, &ready_list, false)) {
+ timeout = 0;
+ progress = true;
}
- /* wait until next event */
- if (aio_epoll_check_poll(ctx, pollfds, npfd, timeout)) {
- AioHandler epoll_handler;
-
- epoll_handler.pfd.fd = ctx->epollfd;
- epoll_handler.pfd.events = G_IO_IN | G_IO_OUT | G_IO_HUP | G_IO_ERR;
- npfd = 0;
- add_pollfd(&epoll_handler);
- ret = aio_epoll(ctx, pollfds, npfd, timeout);
- } else {
- ret = qemu_poll_ns(pollfds, npfd, timeout);
- }
+ ctx->fdmon_ops->wait(ctx, &ready_list, timeout);
}
- if (blocking) {
- atomic_sub(&ctx->notify_me, 2);
- aio_notify_accept(ctx);
+ if (use_notify_me) {
+ /* Finish the poll before clearing the flag. */
+ qatomic_store_release(&ctx->notify_me,
+ qatomic_read(&ctx->notify_me) - 2);
}
+ aio_notify_accept(ctx);
+
/* Adjust polling time */
if (ctx->poll_max_ns) {
int64_t block_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start;
}
}
- /* if we have any readable fds, dispatch event */
- if (ret > 0) {
- for (i = 0; i < npfd; i++) {
- nodes[i]->pfd.revents = pollfds[i].revents;
- }
- }
-
- npfd = 0;
-
progress |= aio_bh_poll(ctx);
+ progress |= aio_dispatch_ready_handlers(ctx, &ready_list);
- if (ret > 0) {
- progress |= aio_dispatch_handlers(ctx);
- }
+ aio_free_deleted_handlers(ctx);
qemu_lockcnt_dec(&ctx->list_lock);
void aio_context_setup(AioContext *ctx)
{
-#ifdef CONFIG_EPOLL_CREATE1
- assert(!ctx->epollfd);
- ctx->epollfd = epoll_create1(EPOLL_CLOEXEC);
- if (ctx->epollfd == -1) {
- fprintf(stderr, "Failed to create epoll instance: %s", strerror(errno));
- ctx->epoll_available = false;
- } else {
- ctx->epoll_available = true;
+ ctx->fdmon_ops = &fdmon_poll_ops;
+ ctx->epollfd = -1;
+
+ /* Use the fastest fd monitoring implementation if available */
+ if (fdmon_io_uring_setup(ctx)) {
+ return;
}
-#endif
+
+ fdmon_epoll_setup(ctx);
}
void aio_context_destroy(AioContext *ctx)
{
-#ifdef CONFIG_EPOLL_CREATE1
- aio_epoll_disable(ctx);
-#endif
+ fdmon_io_uring_destroy(ctx);
+ fdmon_epoll_disable(ctx);
+ aio_free_deleted_handlers(ctx);
+}
+
+void aio_context_use_g_source(AioContext *ctx)
+{
+ /*
+ * Disable io_uring when the glib main loop is used because it doesn't
+ * support mixed glib/aio_poll() usage. It relies on aio_poll() being
+ * called regularly so that changes to the monitored file descriptors are
+ * submitted, otherwise a list of pending fd handlers builds up.
+ */
+ fdmon_io_uring_destroy(ctx);
+ aio_free_deleted_handlers(ctx);
}
void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
aio_notify(ctx);
}
+
+void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch)
+{
+ /*
+ * No thread synchronization here, it doesn't matter if an incorrect value
+ * is used once.
+ */
+ ctx->aio_max_batch = max_batch;
+
+ aio_notify(ctx);
+}
projects / mirror_qemu.git / blobdiff