diff options
Diffstat (limited to 'util/aio-posix.c')
| -rw-r--r-- | util/aio-posix.c | 88 |
1 files changed, 51 insertions, 37 deletions
diff --git a/util/aio-posix.c b/util/aio-posix.c index 131ba6b4a8..621b3025d8 100644 --- a/util/aio-posix.c +++ b/util/aio-posix.c @@ -211,6 +211,7 @@ void aio_set_fd_handler(AioContext *ctx, AioHandler *node; bool is_new = false; bool deleted = false; + int poll_disable_change; qemu_lockcnt_lock(&ctx->list_lock); @@ -244,11 +245,9 @@ void aio_set_fd_handler(AioContext *ctx, QLIST_REMOVE(node, node); deleted = true; } - - if (!node->io_poll) { - ctx->poll_disable_cnt--; - } + poll_disable_change = -!node->io_poll; } else { + poll_disable_change = !io_poll - (node && !node->io_poll); if (node == NULL) { /* Alloc and insert if it's not already there */ node = g_new0(AioHandler, 1); @@ -257,10 +256,6 @@ void aio_set_fd_handler(AioContext *ctx, g_source_add_poll(&ctx->source, &node->pfd); is_new = true; - - ctx->poll_disable_cnt += !io_poll; - } else { - ctx->poll_disable_cnt += !io_poll - !node->io_poll; } /* Update handler with latest information */ @@ -274,6 +269,15 @@ void aio_set_fd_handler(AioContext *ctx, node->pfd.events |= (io_write ? G_IO_OUT | G_IO_ERR : 0); } + /* No need to order poll_disable_cnt writes against other updates; + * the counter is only used to avoid wasting time and latency on + * iterated polling when the system call will be ultimately necessary. + * 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); + aio_epoll_update(ctx, node, is_new); qemu_lockcnt_unlock(&ctx->list_lock); aio_notify(ctx); @@ -486,7 +490,7 @@ static void add_pollfd(AioHandler *node) npfd++; } -static bool run_poll_handlers_once(AioContext *ctx) +static bool run_poll_handlers_once(AioContext *ctx, int64_t *timeout) { bool progress = false; AioHandler *node; @@ -494,9 +498,11 @@ static bool run_poll_handlers_once(AioContext *ctx) 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) && - node->opaque != &ctx->notifier) { - progress = true; + node->io_poll(node->opaque)) { + *timeout = 0; + if (node->opaque != &ctx->notifier) { + progress = true; + } } /* Caller handles freeing deleted nodes. Don't do it here. */ @@ -518,31 +524,38 @@ static bool run_poll_handlers_once(AioContext *ctx) * * Returns: true if progress was made, false otherwise */ -static bool run_poll_handlers(AioContext *ctx, int64_t max_ns) +static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout) { bool progress; - int64_t end_time; + int64_t start_time, elapsed_time; assert(ctx->notify_me); assert(qemu_lockcnt_count(&ctx->list_lock) > 0); - assert(ctx->poll_disable_cnt == 0); - - trace_run_poll_handlers_begin(ctx, max_ns); - end_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + max_ns; + trace_run_poll_handlers_begin(ctx, max_ns, *timeout); + start_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); do { - progress = run_poll_handlers_once(ctx); - } while (!progress && qemu_clock_get_ns(QEMU_CLOCK_REALTIME) < end_time); + progress = run_poll_handlers_once(ctx, timeout); + elapsed_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start_time; + } while (!progress && elapsed_time < max_ns + && !atomic_read(&ctx->poll_disable_cnt)); - trace_run_poll_handlers_end(ctx, progress); + /* If time has passed with no successful polling, adjust *timeout to + * keep the same ending time. + */ + if (*timeout != -1) { + *timeout -= MIN(*timeout, elapsed_time); + } + trace_run_poll_handlers_end(ctx, progress, *timeout); return progress; } /* try_poll_mode: * @ctx: the AioContext - * @blocking: busy polling is only attempted when blocking is true + * @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(). * @@ -550,19 +563,16 @@ static bool run_poll_handlers(AioContext *ctx, int64_t max_ns) * * Returns: true if progress was made, false otherwise */ -static bool try_poll_mode(AioContext *ctx, bool blocking) +static bool try_poll_mode(AioContext *ctx, int64_t *timeout) { - if (blocking && ctx->poll_max_ns && ctx->poll_disable_cnt == 0) { - /* See qemu_soonest_timeout() uint64_t hack */ - int64_t max_ns = MIN((uint64_t)aio_compute_timeout(ctx), - (uint64_t)ctx->poll_ns); + /* See qemu_soonest_timeout() uint64_t hack */ + int64_t max_ns = MIN((uint64_t)*timeout, (uint64_t)ctx->poll_ns); - if (max_ns) { - poll_set_started(ctx, true); + if (max_ns && !atomic_read(&ctx->poll_disable_cnt)) { + poll_set_started(ctx, true); - if (run_poll_handlers(ctx, max_ns)) { - return true; - } + if (run_poll_handlers(ctx, max_ns, timeout)) { + return true; } } @@ -571,7 +581,7 @@ static bool try_poll_mode(AioContext *ctx, bool blocking) /* 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); + return run_poll_handlers_once(ctx, timeout); } bool aio_poll(AioContext *ctx, bool blocking) @@ -601,8 +611,14 @@ bool aio_poll(AioContext *ctx, bool blocking) start = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); } - progress = try_poll_mode(ctx, blocking); - if (!progress) { + timeout = blocking ? aio_compute_timeout(ctx) : 0; + progress = try_poll_mode(ctx, &timeout); + assert(!(timeout && progress)); + + /* 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 */ @@ -616,8 +632,6 @@ bool aio_poll(AioContext *ctx, bool blocking) } } - timeout = blocking ? aio_compute_timeout(ctx) : 0; - /* wait until next event */ if (aio_epoll_check_poll(ctx, pollfds, npfd, timeout)) { AioHandler epoll_handler; |