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![Fam Zheng](/assets/img/avatar_default.png)
To minimize code duplication, epoll is hooked into aio-posix's aio_poll() instead of rolling its own. This approach also has both compile-time and run-time switchability. 1) When QEMU starts with a small number of fds in the event loop, ppoll is used. 2) When QEMU starts with a big number of fds, or when more devices are hot plugged, epoll kicks in when the number of fds hits the threshold. 3) Some fds may not support epoll, such as tty based stdio. In this case, it falls back to ppoll. A rough benchmark with scsi-disk on virtio-scsi dataplane (epoll gets enabled from 64 onward). Numbers are in MB/s. =============================================== | master | epoll | | scsi disks # | read randrw | read randrw -------------|----------------|---------------- 1 | 86 36 | 92 45 8 | 87 43 | 86 41 64 | 71 32 | 70 38 128 | 48 24 | 58 31 256 | 37 19 | 57 28 =============================================== To comply with aio_{disable,enable}_external, we always use ppoll when aio_external_disabled() is true. [Removed #ifdef CONFIG_EPOLL around AioContext epollfd field declaration since the field is also referenced outside CONFIG_EPOLL code. --Stefan] Signed-off-by: Fam Zheng <famz@redhat.com> Message-id: 1446177989-6702-4-git-send-email-famz@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
491 lines
13 KiB
C
491 lines
13 KiB
C
/*
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* QEMU aio implementation
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*
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* Copyright IBM, Corp. 2008
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*
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* Authors:
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* Anthony Liguori <aliguori@us.ibm.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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* Contributions after 2012-01-13 are licensed under the terms of the
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* GNU GPL, version 2 or (at your option) any later version.
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*/
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#include "qemu-common.h"
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#include "block/block.h"
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#include "qemu/queue.h"
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#include "qemu/sockets.h"
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#ifdef CONFIG_EPOLL
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#include <sys/epoll.h>
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#endif
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struct AioHandler
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{
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GPollFD pfd;
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IOHandler *io_read;
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IOHandler *io_write;
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int deleted;
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void *opaque;
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bool is_external;
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QLIST_ENTRY(AioHandler) node;
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};
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#ifdef CONFIG_EPOLL
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/* The fd number threashold to switch to epoll */
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#define EPOLL_ENABLE_THRESHOLD 64
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static void aio_epoll_disable(AioContext *ctx)
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{
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ctx->epoll_available = false;
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if (!ctx->epoll_enabled) {
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return;
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}
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ctx->epoll_enabled = false;
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close(ctx->epollfd);
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}
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static inline int epoll_events_from_pfd(int pfd_events)
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{
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return (pfd_events & G_IO_IN ? EPOLLIN : 0) |
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(pfd_events & G_IO_OUT ? EPOLLOUT : 0) |
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(pfd_events & G_IO_HUP ? EPOLLHUP : 0) |
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(pfd_events & G_IO_ERR ? EPOLLERR : 0);
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}
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static bool aio_epoll_try_enable(AioContext *ctx)
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{
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AioHandler *node;
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struct epoll_event event;
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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int r;
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if (node->deleted || !node->pfd.events) {
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continue;
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}
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event.events = epoll_events_from_pfd(node->pfd.events);
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event.data.ptr = node;
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r = epoll_ctl(ctx->epollfd, EPOLL_CTL_ADD, node->pfd.fd, &event);
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if (r) {
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return false;
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}
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}
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ctx->epoll_enabled = true;
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return true;
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}
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static void aio_epoll_update(AioContext *ctx, AioHandler *node, bool is_new)
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{
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struct epoll_event event;
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int r;
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if (!ctx->epoll_enabled) {
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return;
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}
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if (!node->pfd.events) {
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r = epoll_ctl(ctx->epollfd, EPOLL_CTL_DEL, node->pfd.fd, &event);
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if (r) {
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aio_epoll_disable(ctx);
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}
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} else {
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event.data.ptr = node;
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event.events = epoll_events_from_pfd(node->pfd.events);
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if (is_new) {
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r = epoll_ctl(ctx->epollfd, EPOLL_CTL_ADD, node->pfd.fd, &event);
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if (r) {
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aio_epoll_disable(ctx);
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}
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} else {
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r = epoll_ctl(ctx->epollfd, EPOLL_CTL_MOD, node->pfd.fd, &event);
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if (r) {
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aio_epoll_disable(ctx);
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}
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}
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}
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}
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static int aio_epoll(AioContext *ctx, GPollFD *pfds,
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unsigned npfd, int64_t timeout)
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{
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AioHandler *node;
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int i, ret = 0;
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struct epoll_event events[128];
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assert(npfd == 1);
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assert(pfds[0].fd == ctx->epollfd);
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if (timeout > 0) {
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ret = qemu_poll_ns(pfds, npfd, timeout);
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}
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if (timeout <= 0 || ret > 0) {
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ret = epoll_wait(ctx->epollfd, events,
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sizeof(events) / sizeof(events[0]),
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timeout);
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if (ret <= 0) {
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goto out;
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}
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for (i = 0; i < ret; i++) {
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int ev = events[i].events;
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node = events[i].data.ptr;
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node->pfd.revents = (ev & EPOLLIN ? G_IO_IN : 0) |
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(ev & EPOLLOUT ? G_IO_OUT : 0) |
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(ev & EPOLLHUP ? G_IO_HUP : 0) |
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(ev & EPOLLERR ? G_IO_ERR : 0);
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}
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}
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out:
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return ret;
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}
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static bool aio_epoll_enabled(AioContext *ctx)
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{
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/* Fall back to ppoll when external clients are disabled. */
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return !aio_external_disabled(ctx) && ctx->epoll_enabled;
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}
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static bool aio_epoll_check_poll(AioContext *ctx, GPollFD *pfds,
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unsigned npfd, int64_t timeout)
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{
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if (!ctx->epoll_available) {
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return false;
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}
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if (aio_epoll_enabled(ctx)) {
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return true;
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}
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if (npfd >= EPOLL_ENABLE_THRESHOLD) {
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if (aio_epoll_try_enable(ctx)) {
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return true;
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} else {
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aio_epoll_disable(ctx);
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}
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}
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return false;
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}
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#else
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static void aio_epoll_update(AioContext *ctx, AioHandler *node, bool is_new)
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{
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}
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static int aio_epoll(AioContext *ctx, GPollFD *pfds,
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unsigned npfd, int64_t timeout)
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{
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assert(false);
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}
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static bool aio_epoll_enabled(AioContext *ctx)
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{
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return false;
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}
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static bool aio_epoll_check_poll(AioContext *ctx, GPollFD *pfds,
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unsigned npfd, int64_t timeout)
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{
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return false;
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}
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#endif
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static AioHandler *find_aio_handler(AioContext *ctx, int fd)
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{
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AioHandler *node;
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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if (node->pfd.fd == fd)
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if (!node->deleted)
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return node;
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}
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return NULL;
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}
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void aio_set_fd_handler(AioContext *ctx,
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int fd,
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bool is_external,
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IOHandler *io_read,
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IOHandler *io_write,
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void *opaque)
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{
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AioHandler *node;
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bool is_new = false;
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node = find_aio_handler(ctx, fd);
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/* Are we deleting the fd handler? */
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if (!io_read && !io_write) {
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if (node) {
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g_source_remove_poll(&ctx->source, &node->pfd);
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/* If the lock is held, just mark the node as deleted */
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if (ctx->walking_handlers) {
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node->deleted = 1;
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node->pfd.revents = 0;
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} else {
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/* Otherwise, delete it for real. We can't just mark it as
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* deleted because deleted nodes are only cleaned up after
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* releasing the walking_handlers lock.
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*/
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QLIST_REMOVE(node, node);
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g_free(node);
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}
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}
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} else {
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if (node == NULL) {
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/* Alloc and insert if it's not already there */
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node = g_new0(AioHandler, 1);
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node->pfd.fd = fd;
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QLIST_INSERT_HEAD(&ctx->aio_handlers, node, node);
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g_source_add_poll(&ctx->source, &node->pfd);
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is_new = true;
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}
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/* Update handler with latest information */
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node->io_read = io_read;
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node->io_write = io_write;
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node->opaque = opaque;
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node->is_external = is_external;
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node->pfd.events = (io_read ? G_IO_IN | G_IO_HUP | G_IO_ERR : 0);
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node->pfd.events |= (io_write ? G_IO_OUT | G_IO_ERR : 0);
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}
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aio_epoll_update(ctx, node, is_new);
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aio_notify(ctx);
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}
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void aio_set_event_notifier(AioContext *ctx,
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EventNotifier *notifier,
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bool is_external,
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EventNotifierHandler *io_read)
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{
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aio_set_fd_handler(ctx, event_notifier_get_fd(notifier),
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is_external, (IOHandler *)io_read, NULL, notifier);
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}
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bool aio_prepare(AioContext *ctx)
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{
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return false;
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}
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bool aio_pending(AioContext *ctx)
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{
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AioHandler *node;
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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int revents;
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revents = node->pfd.revents & node->pfd.events;
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if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read) {
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return true;
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}
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if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write) {
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return true;
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}
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}
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return false;
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}
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bool aio_dispatch(AioContext *ctx)
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{
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AioHandler *node;
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bool progress = false;
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/*
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* If there are callbacks left that have been queued, we need to call them.
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* Do not call select in this case, because it is possible that the caller
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* does not need a complete flush (as is the case for aio_poll loops).
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*/
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if (aio_bh_poll(ctx)) {
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progress = true;
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}
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/*
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* We have to walk very carefully in case aio_set_fd_handler is
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* called while we're walking.
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*/
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node = QLIST_FIRST(&ctx->aio_handlers);
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while (node) {
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AioHandler *tmp;
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int revents;
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ctx->walking_handlers++;
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revents = node->pfd.revents & node->pfd.events;
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node->pfd.revents = 0;
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if (!node->deleted &&
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(revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) &&
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node->io_read) {
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node->io_read(node->opaque);
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/* aio_notify() does not count as progress */
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if (node->opaque != &ctx->notifier) {
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progress = true;
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}
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}
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if (!node->deleted &&
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(revents & (G_IO_OUT | G_IO_ERR)) &&
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node->io_write) {
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node->io_write(node->opaque);
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progress = true;
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}
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tmp = node;
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node = QLIST_NEXT(node, node);
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ctx->walking_handlers--;
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if (!ctx->walking_handlers && tmp->deleted) {
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QLIST_REMOVE(tmp, node);
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g_free(tmp);
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}
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}
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/* Run our timers */
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progress |= timerlistgroup_run_timers(&ctx->tlg);
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return progress;
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}
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/* These thread-local variables are used only in a small part of aio_poll
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* around the call to the poll() system call. In particular they are not
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* used while aio_poll is performing callbacks, which makes it much easier
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* to think about reentrancy!
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*
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* Stack-allocated arrays would be perfect but they have size limitations;
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* heap allocation is expensive enough that we want to reuse arrays across
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* calls to aio_poll(). And because poll() has to be called without holding
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* any lock, the arrays cannot be stored in AioContext. Thread-local data
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* has none of the disadvantages of these three options.
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*/
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static __thread GPollFD *pollfds;
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static __thread AioHandler **nodes;
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static __thread unsigned npfd, nalloc;
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static __thread Notifier pollfds_cleanup_notifier;
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static void pollfds_cleanup(Notifier *n, void *unused)
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{
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g_assert(npfd == 0);
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g_free(pollfds);
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g_free(nodes);
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nalloc = 0;
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}
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static void add_pollfd(AioHandler *node)
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{
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if (npfd == nalloc) {
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if (nalloc == 0) {
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pollfds_cleanup_notifier.notify = pollfds_cleanup;
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qemu_thread_atexit_add(&pollfds_cleanup_notifier);
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nalloc = 8;
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} else {
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g_assert(nalloc <= INT_MAX);
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nalloc *= 2;
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}
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pollfds = g_renew(GPollFD, pollfds, nalloc);
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nodes = g_renew(AioHandler *, nodes, nalloc);
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}
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nodes[npfd] = node;
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pollfds[npfd] = (GPollFD) {
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.fd = node->pfd.fd,
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.events = node->pfd.events,
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};
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npfd++;
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}
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bool aio_poll(AioContext *ctx, bool blocking)
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{
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AioHandler *node;
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int i, ret;
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bool progress;
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int64_t timeout;
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aio_context_acquire(ctx);
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progress = false;
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/* aio_notify can avoid the expensive event_notifier_set if
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* everything (file descriptors, bottom halves, timers) will
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* be re-evaluated before the next blocking poll(). This is
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* already true when aio_poll is called with blocking == false;
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* if blocking == true, it is only true after poll() returns,
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* so disable the optimization now.
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*/
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if (blocking) {
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atomic_add(&ctx->notify_me, 2);
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}
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ctx->walking_handlers++;
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assert(npfd == 0);
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/* fill pollfds */
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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if (!node->deleted && node->pfd.events
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&& !aio_epoll_enabled(ctx)
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&& aio_node_check(ctx, node->is_external)) {
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add_pollfd(node);
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}
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}
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timeout = blocking ? aio_compute_timeout(ctx) : 0;
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/* wait until next event */
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if (timeout) {
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aio_context_release(ctx);
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}
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if (aio_epoll_check_poll(ctx, pollfds, npfd, timeout)) {
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AioHandler epoll_handler;
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epoll_handler.pfd.fd = ctx->epollfd;
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epoll_handler.pfd.events = G_IO_IN | G_IO_OUT | G_IO_HUP | G_IO_ERR;
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npfd = 0;
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add_pollfd(&epoll_handler);
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ret = aio_epoll(ctx, pollfds, npfd, timeout);
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} else {
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ret = qemu_poll_ns(pollfds, npfd, timeout);
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}
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if (blocking) {
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atomic_sub(&ctx->notify_me, 2);
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}
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if (timeout) {
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aio_context_acquire(ctx);
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}
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aio_notify_accept(ctx);
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/* if we have any readable fds, dispatch event */
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if (ret > 0) {
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for (i = 0; i < npfd; i++) {
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nodes[i]->pfd.revents = pollfds[i].revents;
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}
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}
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npfd = 0;
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ctx->walking_handlers--;
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/* Run dispatch even if there were no readable fds to run timers */
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if (aio_dispatch(ctx)) {
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progress = true;
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}
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aio_context_release(ctx);
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return progress;
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}
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void aio_context_setup(AioContext *ctx, Error **errp)
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{
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#ifdef CONFIG_EPOLL
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assert(!ctx->epollfd);
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ctx->epollfd = epoll_create1(EPOLL_CLOEXEC);
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if (ctx->epollfd == -1) {
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ctx->epoll_available = false;
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} else {
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ctx->epoll_available = true;
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}
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#endif
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}
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