From 1f050a4690f62a1e7dabc4f44141e9f762c3769f Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Thu, 5 Mar 2020 17:08:02 +0000 Subject: aio-posix: extract ppoll(2) and epoll(7) fd monitoring The ppoll(2) and epoll(7) file descriptor monitoring implementations are mixed with the core util/aio-posix.c code. Before adding another implementation for Linux io_uring, extract out the existing ones so there is a clear interface and the core code is simpler. The new interface is AioContext->fdmon_ops, a pointer to a FDMonOps struct. See the patch for details. Semantic changes: 1. ppoll(2) now reflects events from pollfds[] back into AioHandlers while we're still on the clock for adaptive polling. This was already happening for epoll(7), so if it's really an issue then we'll need to fix both in the future. 2. epoll(7)'s fallback to ppoll(2) while external events are disabled was broken when the number of fds exceeded the epoll(7) upgrade threshold. I guess this code path simply wasn't tested and no one noticed the bug. I didn't go out of my way to fix it but the correct code is simpler than preserving the bug. I also took some liberties in removing the unnecessary AioContext->epoll_available (just check AioContext->epollfd != -1 instead) and AioContext->epoll_enabled (it's implicit if our AioContext->fdmon_ops callbacks are being invoked) fields. Signed-off-by: Stefan Hajnoczi Link: https://lore.kernel.org/r/20200305170806.1313245-4-stefanha@redhat.com Message-Id: <20200305170806.1313245-4-stefanha@redhat.com> --- util/fdmon-epoll.c | 151 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 151 insertions(+) create mode 100644 util/fdmon-epoll.c (limited to 'util/fdmon-epoll.c') diff --git a/util/fdmon-epoll.c b/util/fdmon-epoll.c new file mode 100644 index 0000000000..29c1454469 --- /dev/null +++ b/util/fdmon-epoll.c @@ -0,0 +1,151 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * epoll(7) file descriptor monitoring + */ + +#include "qemu/osdep.h" +#include +#include "qemu/rcu_queue.h" +#include "aio-posix.h" + +/* The fd number threshold to switch to epoll */ +#define EPOLL_ENABLE_THRESHOLD 64 + +void fdmon_epoll_disable(AioContext *ctx) +{ + if (ctx->epollfd >= 0) { + close(ctx->epollfd); + ctx->epollfd = -1; + } + + /* Switch back */ + ctx->fdmon_ops = &fdmon_poll_ops; +} + +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 void fdmon_epoll_update(AioContext *ctx, AioHandler *node, bool is_new) +{ + struct epoll_event event; + int r; + int ctl; + + 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) { + fdmon_epoll_disable(ctx); + } +} + +static int fdmon_epoll_wait(AioContext *ctx, AioHandlerList *ready_list, + int64_t timeout) +{ + GPollFD pfd = { + .fd = ctx->epollfd, + .events = G_IO_IN | G_IO_OUT | G_IO_HUP | G_IO_ERR, + }; + AioHandler *node; + int i, ret = 0; + struct epoll_event events[128]; + + /* Fall back while external clients are disabled */ + if (atomic_read(&ctx->external_disable_cnt)) { + return fdmon_poll_ops.wait(ctx, ready_list, timeout); + } + + if (timeout > 0) { + ret = qemu_poll_ns(&pfd, 1, timeout); + if (ret > 0) { + timeout = 0; + } + } + 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; + int 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); + + node = events[i].data.ptr; + aio_add_ready_handler(ready_list, node, revents); + } + } +out: + return ret; +} + +static const FDMonOps fdmon_epoll_ops = { + .update = fdmon_epoll_update, + .wait = fdmon_epoll_wait, +}; + +static bool fdmon_epoll_try_enable(AioContext *ctx) +{ + AioHandler *node; + struct epoll_event event; + + QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) { + int r; + if (QLIST_IS_INSERTED(node, 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->fdmon_ops = &fdmon_epoll_ops; + return true; +} + +bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd) +{ + if (ctx->epollfd < 0) { + return false; + } + + /* Do not upgrade while external clients are disabled */ + if (atomic_read(&ctx->external_disable_cnt)) { + return false; + } + + if (npfd >= EPOLL_ENABLE_THRESHOLD) { + if (fdmon_epoll_try_enable(ctx)) { + return true; + } else { + fdmon_epoll_disable(ctx); + } + } + return false; +} + +void fdmon_epoll_setup(AioContext *ctx) +{ + ctx->epollfd = epoll_create1(EPOLL_CLOEXEC); + if (ctx->epollfd == -1) { + fprintf(stderr, "Failed to create epoll instance: %s", strerror(errno)); + } +} -- cgit v1.2.3