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aio-posix: support userspace polling of fd monitoring
Unlike ppoll(2) and epoll(7), Linux io_uring completions can be polled from userspace. Previously userspace polling was only allowed when all AioHandler's had an ->io_poll() callback. This prevented starvation of fds by userspace pollable handlers. Add the FDMonOps->need_wait() callback that enables userspace polling even when some AioHandlers lack ->io_poll(). For example, it's now possible to do userspace polling when a TCP/IP socket is monitored thanks to Linux io_uring. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Link: https://lore.kernel.org/r/20200305170806.1313245-7-stefanha@redhat.com Message-Id: <20200305170806.1313245-7-stefanha@redhat.com>
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@ -55,6 +55,9 @@ struct ThreadPool;
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struct LinuxAioState;
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struct LinuxAioState;
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struct LuringState;
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struct LuringState;
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/* Is polling disabled? */
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bool aio_poll_disabled(AioContext *ctx);
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/* Callbacks for file descriptor monitoring implementations */
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/* Callbacks for file descriptor monitoring implementations */
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typedef struct {
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typedef struct {
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/*
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/*
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@ -84,6 +87,22 @@ typedef struct {
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* Returns: number of ready file descriptors.
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* Returns: number of ready file descriptors.
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*/
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*/
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int (*wait)(AioContext *ctx, AioHandlerList *ready_list, int64_t timeout);
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int (*wait)(AioContext *ctx, AioHandlerList *ready_list, int64_t timeout);
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/*
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* need_wait:
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* @ctx: the AioContext
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*
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* Tell aio_poll() when to stop userspace polling early because ->wait()
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* has fds ready.
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*
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* File descriptor monitoring implementations that cannot poll fd readiness
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* from userspace should use aio_poll_disabled() here. This ensures that
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* file descriptors are not starved by handlers that frequently make
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* progress via userspace polling.
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*
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* Returns: true if ->wait() should be called, false otherwise.
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*/
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bool (*need_wait)(AioContext *ctx);
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} FDMonOps;
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} FDMonOps;
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/*
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/*
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@ -22,6 +22,11 @@
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#include "trace.h"
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#include "trace.h"
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#include "aio-posix.h"
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#include "aio-posix.h"
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bool aio_poll_disabled(AioContext *ctx)
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{
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return atomic_read(&ctx->poll_disable_cnt);
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}
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void aio_add_ready_handler(AioHandlerList *ready_list,
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void aio_add_ready_handler(AioHandlerList *ready_list,
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AioHandler *node,
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AioHandler *node,
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int revents)
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int revents)
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@ -423,7 +428,7 @@ static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout)
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elapsed_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start_time;
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elapsed_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start_time;
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max_ns = qemu_soonest_timeout(*timeout, max_ns);
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max_ns = qemu_soonest_timeout(*timeout, max_ns);
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assert(!(max_ns && progress));
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assert(!(max_ns && progress));
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} while (elapsed_time < max_ns && !atomic_read(&ctx->poll_disable_cnt));
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} while (elapsed_time < max_ns && !ctx->fdmon_ops->need_wait(ctx));
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/* If time has passed with no successful polling, adjust *timeout to
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/* If time has passed with no successful polling, adjust *timeout to
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* keep the same ending time.
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* keep the same ending time.
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@ -451,7 +456,7 @@ static bool try_poll_mode(AioContext *ctx, int64_t *timeout)
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{
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{
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int64_t max_ns = qemu_soonest_timeout(*timeout, ctx->poll_ns);
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int64_t max_ns = qemu_soonest_timeout(*timeout, ctx->poll_ns);
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if (max_ns && !atomic_read(&ctx->poll_disable_cnt)) {
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if (max_ns && !ctx->fdmon_ops->need_wait(ctx)) {
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poll_set_started(ctx, true);
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poll_set_started(ctx, true);
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if (run_poll_handlers(ctx, max_ns, timeout)) {
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if (run_poll_handlers(ctx, max_ns, timeout)) {
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@ -501,7 +506,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
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/* If polling is allowed, non-blocking aio_poll does not need the
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/* If polling is allowed, non-blocking aio_poll does not need the
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* system call---a single round of run_poll_handlers_once suffices.
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* system call---a single round of run_poll_handlers_once suffices.
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*/
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*/
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if (timeout || atomic_read(&ctx->poll_disable_cnt)) {
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if (timeout || ctx->fdmon_ops->need_wait(ctx)) {
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ret = ctx->fdmon_ops->wait(ctx, &ready_list, timeout);
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ret = ctx->fdmon_ops->wait(ctx, &ready_list, timeout);
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}
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}
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@ -100,6 +100,7 @@ out:
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static const FDMonOps fdmon_epoll_ops = {
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static const FDMonOps fdmon_epoll_ops = {
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.update = fdmon_epoll_update,
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.update = fdmon_epoll_update,
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.wait = fdmon_epoll_wait,
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.wait = fdmon_epoll_wait,
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.need_wait = aio_poll_disabled,
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};
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};
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static bool fdmon_epoll_try_enable(AioContext *ctx)
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static bool fdmon_epoll_try_enable(AioContext *ctx)
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@ -288,9 +288,15 @@ static int fdmon_io_uring_wait(AioContext *ctx, AioHandlerList *ready_list,
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return process_cq_ring(ctx, ready_list);
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return process_cq_ring(ctx, ready_list);
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}
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}
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static bool fdmon_io_uring_need_wait(AioContext *ctx)
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{
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return io_uring_cq_ready(&ctx->fdmon_io_uring);
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}
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static const FDMonOps fdmon_io_uring_ops = {
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static const FDMonOps fdmon_io_uring_ops = {
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.update = fdmon_io_uring_update,
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.update = fdmon_io_uring_update,
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.wait = fdmon_io_uring_wait,
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.wait = fdmon_io_uring_wait,
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.need_wait = fdmon_io_uring_need_wait,
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};
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};
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bool fdmon_io_uring_setup(AioContext *ctx)
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bool fdmon_io_uring_setup(AioContext *ctx)
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@ -103,4 +103,5 @@ static void fdmon_poll_update(AioContext *ctx,
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const FDMonOps fdmon_poll_ops = {
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const FDMonOps fdmon_poll_ops = {
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.update = fdmon_poll_update,
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.update = fdmon_poll_update,
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.wait = fdmon_poll_wait,
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.wait = fdmon_poll_wait,
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.need_wait = aio_poll_disabled,
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};
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};
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