740 lines
19 KiB
C
740 lines
19 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/osdep.h"
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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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#include "qemu/cutils.h"
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#include "trace.h"
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#ifdef CONFIG_EPOLL_CREATE1
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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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AioPollFn *io_poll;
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IOHandler *io_poll_begin;
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IOHandler *io_poll_end;
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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_CREATE1
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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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int ctl;
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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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ctl = EPOLL_CTL_DEL;
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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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ctl = is_new ? EPOLL_CTL_ADD : EPOLL_CTL_MOD;
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}
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r = epoll_ctl(ctx->epollfd, ctl, 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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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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AioPollFn *io_poll,
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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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bool deleted = 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 && !io_poll) {
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if (node == NULL) {
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return;
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}
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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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deleted = true;
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}
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if (!node->io_poll) {
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ctx->poll_disable_cnt--;
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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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ctx->poll_disable_cnt += !io_poll;
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} else {
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ctx->poll_disable_cnt += !io_poll - !node->io_poll;
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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->io_poll = io_poll;
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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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if (deleted) {
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g_free(node);
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}
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}
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void aio_set_fd_poll(AioContext *ctx, int fd,
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IOHandler *io_poll_begin,
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IOHandler *io_poll_end)
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{
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AioHandler *node = find_aio_handler(ctx, fd);
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if (!node) {
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return;
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}
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node->io_poll_begin = io_poll_begin;
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node->io_poll_end = io_poll_end;
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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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AioPollFn *io_poll)
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{
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aio_set_fd_handler(ctx, event_notifier_get_fd(notifier), is_external,
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(IOHandler *)io_read, NULL, io_poll, notifier);
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}
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void aio_set_event_notifier_poll(AioContext *ctx,
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EventNotifier *notifier,
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EventNotifierHandler *io_poll_begin,
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EventNotifierHandler *io_poll_end)
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{
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aio_set_fd_poll(ctx, event_notifier_get_fd(notifier),
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(IOHandler *)io_poll_begin,
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(IOHandler *)io_poll_end);
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}
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static void poll_set_started(AioContext *ctx, bool started)
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{
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AioHandler *node;
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if (started == ctx->poll_started) {
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return;
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}
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ctx->poll_started = started;
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ctx->walking_handlers++;
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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IOHandler *fn;
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if (node->deleted) {
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continue;
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}
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if (started) {
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fn = node->io_poll_begin;
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} else {
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fn = node->io_poll_end;
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}
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if (fn) {
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fn(node->opaque);
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}
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}
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ctx->walking_handlers--;
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}
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bool aio_prepare(AioContext *ctx)
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{
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/* Poll mode cannot be used with glib's event loop, disable it. */
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poll_set_started(ctx, false);
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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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aio_node_check(ctx, node->is_external)) {
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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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aio_node_check(ctx, node->is_external)) {
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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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/*
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* Note that dispatch_fds == false has the side-effect of post-poning the
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* freeing of deleted handlers.
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*/
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bool aio_dispatch(AioContext *ctx, bool dispatch_fds)
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{
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AioHandler *node = NULL;
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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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if (dispatch_fds) {
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node = QLIST_FIRST(&ctx->aio_handlers);
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}
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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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aio_node_check(ctx, node->is_external) &&
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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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aio_node_check(ctx, node->is_external) &&
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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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static bool run_poll_handlers_once(AioContext *ctx)
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{
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bool progress = false;
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AioHandler *node;
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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if (!node->deleted && node->io_poll &&
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node->io_poll(node->opaque)) {
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progress = true;
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}
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/* Caller handles freeing deleted nodes. Don't do it here. */
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}
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return progress;
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}
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/* run_poll_handlers:
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* @ctx: the AioContext
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* @max_ns: maximum time to poll for, in nanoseconds
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*
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* Polls for a given time.
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*
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* Note that ctx->notify_me must be non-zero so this function can detect
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* aio_notify().
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*
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* Note that the caller must have incremented ctx->walking_handlers.
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*
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* Returns: true if progress was made, false otherwise
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*/
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static bool run_poll_handlers(AioContext *ctx, int64_t max_ns)
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{
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bool progress;
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int64_t end_time;
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assert(ctx->notify_me);
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assert(ctx->walking_handlers > 0);
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assert(ctx->poll_disable_cnt == 0);
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trace_run_poll_handlers_begin(ctx, max_ns);
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end_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + max_ns;
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do {
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progress = run_poll_handlers_once(ctx);
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} while (!progress && qemu_clock_get_ns(QEMU_CLOCK_REALTIME) < end_time);
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trace_run_poll_handlers_end(ctx, progress);
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return progress;
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}
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/* try_poll_mode:
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* @ctx: the AioContext
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* @blocking: busy polling is only attempted when blocking is true
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*
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* ctx->notify_me must be non-zero so this function can detect aio_notify().
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*
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* Note that the caller must have incremented ctx->walking_handlers.
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*
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* Returns: true if progress was made, false otherwise
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*/
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static bool try_poll_mode(AioContext *ctx, bool blocking)
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{
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if (blocking && ctx->poll_max_ns && ctx->poll_disable_cnt == 0) {
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/* See qemu_soonest_timeout() uint64_t hack */
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int64_t max_ns = MIN((uint64_t)aio_compute_timeout(ctx),
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(uint64_t)ctx->poll_ns);
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if (max_ns) {
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poll_set_started(ctx, true);
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if (run_poll_handlers(ctx, max_ns)) {
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return true;
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}
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}
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}
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poll_set_started(ctx, false);
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/* Even if we don't run busy polling, try polling once in case it can make
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* progress and the caller will be able to avoid ppoll(2)/epoll_wait(2).
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*/
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return run_poll_handlers_once(ctx);
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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;
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int ret = 0;
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bool progress;
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int64_t timeout;
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int64_t start = 0;
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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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|
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ctx->walking_handlers++;
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|
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if (ctx->poll_max_ns) {
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start = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
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}
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|
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if (try_poll_mode(ctx, blocking)) {
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progress = true;
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} else {
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assert(npfd == 0);
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|
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/* fill pollfds */
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|
|
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if (!aio_epoll_enabled(ctx)) {
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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_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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}
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timeout = blocking ? aio_compute_timeout(ctx) : 0;
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|
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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);
|
|
}
|
|
if (timeout) {
|
|
aio_context_acquire(ctx);
|
|
}
|
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}
|
|
|
|
if (blocking) {
|
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atomic_sub(&ctx->notify_me, 2);
|
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}
|
|
|
|
/* 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);
|
|
}
|
|
}
|
|
|
|
aio_notify_accept(ctx);
|
|
|
|
/* 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;
|
|
ctx->walking_handlers--;
|
|
|
|
/* Run dispatch even if there were no readable fds to run timers */
|
|
if (aio_dispatch(ctx, ret > 0)) {
|
|
progress = true;
|
|
}
|
|
|
|
aio_context_release(ctx);
|
|
|
|
return progress;
|
|
}
|
|
|
|
void aio_context_setup(AioContext *ctx)
|
|
{
|
|
/* TODO remove this in final patch submission */
|
|
if (getenv("QEMU_AIO_POLL_MAX_NS")) {
|
|
fprintf(stderr, "The QEMU_AIO_POLL_MAX_NS environment variable has "
|
|
"been replaced with -object iothread,poll-max-ns=NUM\n");
|
|
exit(1);
|
|
}
|
|
|
|
#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_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);
|
|
}
|