/* * QEMU aio implementation * * Copyright IBM, Corp. 2008 * * Authors: * Anthony Liguori * * This work is licensed under the terms of the GNU GPL, version 2. See * the COPYING file in the top-level directory. * * Contributions after 2012-01-13 are licensed under the terms of the * GNU GPL, version 2 or (at your option) any later version. */ #include "qemu/osdep.h" #include "qemu-common.h" #include "block/block.h" #include "qemu/rcu_queue.h" #include "qemu/sockets.h" #include "qemu/cutils.h" #include "trace.h" #ifdef CONFIG_EPOLL_CREATE1 #include #endif 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 threashold 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); } } static int aio_epoll(AioContext *ctx, GPollFD *pfds, unsigned npfd, int64_t timeout) { 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; } static bool aio_epoll_enabled(AioContext *ctx) { /* Fall back to ppoll when external clients are disabled. */ return !aio_external_disabled(ctx) && ctx->epoll_enabled; } static bool aio_epoll_check_poll(AioContext *ctx, GPollFD *pfds, unsigned npfd, int64_t timeout) { 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; } #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) return node; } return NULL; } void aio_set_fd_handler(AioContext *ctx, int fd, bool is_external, IOHandler *io_read, IOHandler *io_write, AioPollFn *io_poll, void *opaque) { AioHandler *node; bool is_new = false; bool deleted = false; int poll_disable_change; qemu_lockcnt_lock(&ctx->list_lock); node = find_aio_handler(ctx, fd); /* Are we deleting the fd handler? */ if (!io_read && !io_write && !io_poll) { if (node == NULL) { qemu_lockcnt_unlock(&ctx->list_lock); return; } /* If the GSource is in the process of being destroyed then * g_source_remove_poll() causes an assertion failure. Skip * removal in that case, because glib cleans up its state during * destruction anyway. */ if (!g_source_is_destroyed(&ctx->source)) { g_source_remove_poll(&ctx->source, &node->pfd); } /* 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; } else { /* 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_REMOVE(node, node); deleted = true; } 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); node->pfd.fd = fd; QLIST_INSERT_HEAD_RCU(&ctx->aio_handlers, node, node); g_source_add_poll(&ctx->source, &node->pfd); is_new = true; } /* Update handler with latest information */ node->io_read = io_read; node->io_write = io_write; node->io_poll = io_poll; node->opaque = opaque; node->is_external = is_external; node->pfd.events = (io_read ? G_IO_IN | G_IO_HUP | G_IO_ERR : 0); 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); if (deleted) { g_free(node); } } void aio_set_fd_poll(AioContext *ctx, int fd, IOHandler *io_poll_begin, IOHandler *io_poll_end) { AioHandler *node = find_aio_handler(ctx, fd); if (!node) { return; } node->io_poll_begin = io_poll_begin; node->io_poll_end = io_poll_end; } void aio_set_event_notifier(AioContext *ctx, EventNotifier *notifier, bool is_external, EventNotifierHandler *io_read, AioPollFn *io_poll) { aio_set_fd_handler(ctx, event_notifier_get_fd(notifier), is_external, (IOHandler *)io_read, NULL, io_poll, notifier); } void aio_set_event_notifier_poll(AioContext *ctx, EventNotifier *notifier, EventNotifierHandler *io_poll_begin, EventNotifierHandler *io_poll_end) { aio_set_fd_poll(ctx, event_notifier_get_fd(notifier), (IOHandler *)io_poll_begin, (IOHandler *)io_poll_end); } static void poll_set_started(AioContext *ctx, bool started) { AioHandler *node; if (started == ctx->poll_started) { return; } ctx->poll_started = started; qemu_lockcnt_inc(&ctx->list_lock); QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) { IOHandler *fn; if (node->deleted) { continue; } if (started) { fn = node->io_poll_begin; } else { fn = node->io_poll_end; } if (fn) { fn(node->opaque); } } qemu_lockcnt_dec(&ctx->list_lock); } bool aio_prepare(AioContext *ctx) { /* Poll mode cannot be used with glib's event loop, disable it. */ poll_set_started(ctx, false); return false; } bool aio_pending(AioContext *ctx) { AioHandler *node; bool result = false; /* * We have to walk very carefully in case aio_set_fd_handler is * called while we're walking. */ qemu_lockcnt_inc(&ctx->list_lock); QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) { int revents; 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)) { result = true; break; } if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write && aio_node_check(ctx, node->is_external)) { result = true; break; } } qemu_lockcnt_dec(&ctx->list_lock); return result; } static bool aio_dispatch_handlers(AioContext *ctx) { AioHandler *node, *tmp; bool progress = false; QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) { int revents; revents = node->pfd.revents & node->pfd.events; node->pfd.revents = 0; 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); /* aio_notify() does not count as progress */ if (node->opaque != &ctx->notifier) { progress = true; } } 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); 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; } void aio_dispatch(AioContext *ctx) { qemu_lockcnt_inc(&ctx->list_lock); aio_bh_poll(ctx); aio_dispatch_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) { bool progress = false; AioHandler *node; 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)) { *timeout = 0; if (node->opaque != &ctx->notifier) { progress = true; } } /* Caller handles freeing deleted nodes. Don't do it here. */ } return progress; } /* run_poll_handlers: * @ctx: the AioContext * @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) { 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); start_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); do { 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)); /* 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 * @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) { /* See qemu_soonest_timeout() uint64_t hack */ int64_t max_ns = MIN((uint64_t)*timeout, (uint64_t)ctx->poll_ns); if (max_ns && !atomic_read(&ctx->poll_disable_cnt)) { poll_set_started(ctx, true); if (run_poll_handlers(ctx, 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); } bool aio_poll(AioContext *ctx, bool blocking) { AioHandler *node; int i; int ret = 0; bool progress; int64_t timeout; int64_t start = 0; /* 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. */ if (blocking) { assert(in_aio_context_home_thread(ctx)); atomic_add(&ctx->notify_me, 2); } qemu_lockcnt_inc(&ctx->list_lock); if (ctx->poll_max_ns) { start = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); } 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 */ 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); } } } /* 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); } } if (blocking) { atomic_sub(&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 (block_ns <= ctx->poll_ns) { /* This is the sweet spot, no adjustment needed */ } else if (block_ns > ctx->poll_max_ns) { /* We'd have to poll for too long, poll less */ int64_t old = ctx->poll_ns; if (ctx->poll_shrink) { ctx->poll_ns /= ctx->poll_shrink; } else { ctx->poll_ns = 0; } trace_poll_shrink(ctx, old, ctx->poll_ns); } else if (ctx->poll_ns < ctx->poll_max_ns && block_ns < ctx->poll_max_ns) { /* There is room to grow, poll longer */ int64_t old = ctx->poll_ns; int64_t grow = ctx->poll_grow; if (grow == 0) { grow = 2; } if (ctx->poll_ns) { ctx->poll_ns *= grow; } else { ctx->poll_ns = 4000; /* start polling at 4 microseconds */ } if (ctx->poll_ns > ctx->poll_max_ns) { ctx->poll_ns = ctx->poll_max_ns; } trace_poll_grow(ctx, old, ctx->poll_ns); } } /* 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); if (ret > 0) { progress |= aio_dispatch_handlers(ctx); } qemu_lockcnt_dec(&ctx->list_lock); progress |= timerlistgroup_run_timers(&ctx->tlg); return progress; } 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; } #endif } void aio_context_destroy(AioContext *ctx) { #ifdef CONFIG_EPOLL_CREATE1 aio_epoll_disable(ctx); #endif } void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns, int64_t grow, int64_t shrink, Error **errp) { /* No thread synchronization here, it doesn't matter if an incorrect value * is used once. */ ctx->poll_max_ns = max_ns; ctx->poll_ns = 0; ctx->poll_grow = grow; ctx->poll_shrink = shrink; aio_notify(ctx); }