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https://gitlab.com/qemu-project/qemu
synced 2024-09-06 18:05:37 +00:00
![Anthony Liguori](/assets/img/avatar_default.png)
The char-flow refactoring introduced a busy-wait that depended on an action from the VCPU thread. However, the VCPU thread could never take that action because the busy-wait starved the VCPU thread of the BQL because it never dropped the mutex while running select. Paolo doesn't want to drop this optimization for fear that we will stop detecting these busy waits. I'm afraid to keep this optimization even with the busy-wait fixed because I think a similar problem can occur just with heavy I/O thread load manifesting itself as VCPU pauses. As a compromise, introduce an artificial timeout after a thousand iterations but print a rate limited warning when this happens. This let's us still detect when this condition occurs without it being a fatal error. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> Message-id: 1365169560-11012-1-git-send-email-aliguori@us.ibm.com
509 lines
13 KiB
C
509 lines
13 KiB
C
/*
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* QEMU System Emulator
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*
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* Copyright (c) 2003-2008 Fabrice Bellard
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#include "qemu-common.h"
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#include "qemu/timer.h"
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#include "slirp/slirp.h"
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#include "qemu/main-loop.h"
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#include "block/aio.h"
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#ifndef _WIN32
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#include "qemu/compatfd.h"
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/* If we have signalfd, we mask out the signals we want to handle and then
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* use signalfd to listen for them. We rely on whatever the current signal
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* handler is to dispatch the signals when we receive them.
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*/
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static void sigfd_handler(void *opaque)
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{
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int fd = (intptr_t)opaque;
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struct qemu_signalfd_siginfo info;
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struct sigaction action;
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ssize_t len;
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while (1) {
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do {
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len = read(fd, &info, sizeof(info));
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} while (len == -1 && errno == EINTR);
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if (len == -1 && errno == EAGAIN) {
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break;
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}
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if (len != sizeof(info)) {
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printf("read from sigfd returned %zd: %m\n", len);
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return;
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}
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sigaction(info.ssi_signo, NULL, &action);
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if ((action.sa_flags & SA_SIGINFO) && action.sa_sigaction) {
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action.sa_sigaction(info.ssi_signo,
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(siginfo_t *)&info, NULL);
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} else if (action.sa_handler) {
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action.sa_handler(info.ssi_signo);
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}
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}
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}
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static int qemu_signal_init(void)
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{
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int sigfd;
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sigset_t set;
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/*
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* SIG_IPI must be blocked in the main thread and must not be caught
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* by sigwait() in the signal thread. Otherwise, the cpu thread will
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* not catch it reliably.
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*/
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sigemptyset(&set);
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sigaddset(&set, SIG_IPI);
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sigaddset(&set, SIGIO);
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sigaddset(&set, SIGALRM);
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sigaddset(&set, SIGBUS);
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pthread_sigmask(SIG_BLOCK, &set, NULL);
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sigdelset(&set, SIG_IPI);
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sigfd = qemu_signalfd(&set);
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if (sigfd == -1) {
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fprintf(stderr, "failed to create signalfd\n");
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return -errno;
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}
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fcntl_setfl(sigfd, O_NONBLOCK);
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qemu_set_fd_handler2(sigfd, NULL, sigfd_handler, NULL,
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(void *)(intptr_t)sigfd);
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return 0;
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}
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#else /* _WIN32 */
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static int qemu_signal_init(void)
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{
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return 0;
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}
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#endif
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static AioContext *qemu_aio_context;
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AioContext *qemu_get_aio_context(void)
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{
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return qemu_aio_context;
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}
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void qemu_notify_event(void)
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{
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if (!qemu_aio_context) {
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return;
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}
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aio_notify(qemu_aio_context);
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}
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static GArray *gpollfds;
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int qemu_init_main_loop(void)
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{
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int ret;
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GSource *src;
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init_clocks();
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if (init_timer_alarm() < 0) {
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fprintf(stderr, "could not initialize alarm timer\n");
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exit(1);
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}
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ret = qemu_signal_init();
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if (ret) {
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return ret;
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}
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gpollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
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qemu_aio_context = aio_context_new();
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src = aio_get_g_source(qemu_aio_context);
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g_source_attach(src, NULL);
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g_source_unref(src);
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return 0;
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}
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static int max_priority;
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#ifndef _WIN32
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static int glib_pollfds_idx;
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static int glib_n_poll_fds;
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static void glib_pollfds_fill(uint32_t *cur_timeout)
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{
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GMainContext *context = g_main_context_default();
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int timeout = 0;
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int n;
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g_main_context_prepare(context, &max_priority);
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glib_pollfds_idx = gpollfds->len;
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n = glib_n_poll_fds;
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do {
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GPollFD *pfds;
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glib_n_poll_fds = n;
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g_array_set_size(gpollfds, glib_pollfds_idx + glib_n_poll_fds);
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pfds = &g_array_index(gpollfds, GPollFD, glib_pollfds_idx);
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n = g_main_context_query(context, max_priority, &timeout, pfds,
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glib_n_poll_fds);
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} while (n != glib_n_poll_fds);
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if (timeout >= 0 && timeout < *cur_timeout) {
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*cur_timeout = timeout;
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}
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}
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static void glib_pollfds_poll(void)
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{
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GMainContext *context = g_main_context_default();
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GPollFD *pfds = &g_array_index(gpollfds, GPollFD, glib_pollfds_idx);
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if (g_main_context_check(context, max_priority, pfds, glib_n_poll_fds)) {
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g_main_context_dispatch(context);
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}
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}
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#define MAX_MAIN_LOOP_SPIN (1000)
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static int os_host_main_loop_wait(uint32_t timeout)
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{
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int ret;
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static int spin_counter;
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glib_pollfds_fill(&timeout);
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/* If the I/O thread is very busy or we are incorrectly busy waiting in
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* the I/O thread, this can lead to starvation of the BQL such that the
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* VCPU threads never run. To make sure we can detect the later case,
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* print a message to the screen. If we run into this condition, create
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* a fake timeout in order to give the VCPU threads a chance to run.
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*/
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if (spin_counter > MAX_MAIN_LOOP_SPIN) {
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static bool notified;
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if (!notified) {
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fprintf(stderr,
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"main-loop: WARNING: I/O thread spun for %d iterations\n",
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MAX_MAIN_LOOP_SPIN);
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notified = true;
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}
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timeout = 1;
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}
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if (timeout > 0) {
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spin_counter = 0;
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qemu_mutex_unlock_iothread();
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} else {
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spin_counter++;
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}
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ret = g_poll((GPollFD *)gpollfds->data, gpollfds->len, timeout);
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if (timeout > 0) {
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qemu_mutex_lock_iothread();
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}
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glib_pollfds_poll();
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return ret;
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}
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#else
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/***********************************************************/
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/* Polling handling */
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typedef struct PollingEntry {
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PollingFunc *func;
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void *opaque;
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struct PollingEntry *next;
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} PollingEntry;
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static PollingEntry *first_polling_entry;
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int qemu_add_polling_cb(PollingFunc *func, void *opaque)
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{
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PollingEntry **ppe, *pe;
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pe = g_malloc0(sizeof(PollingEntry));
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pe->func = func;
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pe->opaque = opaque;
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for(ppe = &first_polling_entry; *ppe != NULL; ppe = &(*ppe)->next);
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*ppe = pe;
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return 0;
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}
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void qemu_del_polling_cb(PollingFunc *func, void *opaque)
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{
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PollingEntry **ppe, *pe;
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for(ppe = &first_polling_entry; *ppe != NULL; ppe = &(*ppe)->next) {
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pe = *ppe;
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if (pe->func == func && pe->opaque == opaque) {
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*ppe = pe->next;
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g_free(pe);
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break;
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}
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}
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}
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/***********************************************************/
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/* Wait objects support */
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typedef struct WaitObjects {
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int num;
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int revents[MAXIMUM_WAIT_OBJECTS + 1];
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HANDLE events[MAXIMUM_WAIT_OBJECTS + 1];
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WaitObjectFunc *func[MAXIMUM_WAIT_OBJECTS + 1];
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void *opaque[MAXIMUM_WAIT_OBJECTS + 1];
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} WaitObjects;
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static WaitObjects wait_objects = {0};
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int qemu_add_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
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{
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WaitObjects *w = &wait_objects;
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if (w->num >= MAXIMUM_WAIT_OBJECTS) {
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return -1;
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}
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w->events[w->num] = handle;
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w->func[w->num] = func;
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w->opaque[w->num] = opaque;
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w->revents[w->num] = 0;
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w->num++;
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return 0;
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}
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void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
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{
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int i, found;
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WaitObjects *w = &wait_objects;
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found = 0;
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for (i = 0; i < w->num; i++) {
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if (w->events[i] == handle) {
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found = 1;
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}
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if (found) {
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w->events[i] = w->events[i + 1];
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w->func[i] = w->func[i + 1];
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w->opaque[i] = w->opaque[i + 1];
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w->revents[i] = w->revents[i + 1];
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}
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}
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if (found) {
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w->num--;
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}
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}
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void qemu_fd_register(int fd)
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{
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WSAEventSelect(fd, event_notifier_get_handle(&qemu_aio_context->notifier),
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FD_READ | FD_ACCEPT | FD_CLOSE |
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FD_CONNECT | FD_WRITE | FD_OOB);
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}
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static int pollfds_fill(GArray *pollfds, fd_set *rfds, fd_set *wfds,
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fd_set *xfds)
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{
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int nfds = -1;
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int i;
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for (i = 0; i < pollfds->len; i++) {
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GPollFD *pfd = &g_array_index(pollfds, GPollFD, i);
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int fd = pfd->fd;
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int events = pfd->events;
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if (events & (G_IO_IN | G_IO_HUP | G_IO_ERR)) {
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FD_SET(fd, rfds);
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nfds = MAX(nfds, fd);
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}
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if (events & (G_IO_OUT | G_IO_ERR)) {
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FD_SET(fd, wfds);
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nfds = MAX(nfds, fd);
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}
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if (events & G_IO_PRI) {
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FD_SET(fd, xfds);
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nfds = MAX(nfds, fd);
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}
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}
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return nfds;
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}
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static void pollfds_poll(GArray *pollfds, int nfds, fd_set *rfds,
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fd_set *wfds, fd_set *xfds)
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{
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int i;
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for (i = 0; i < pollfds->len; i++) {
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GPollFD *pfd = &g_array_index(pollfds, GPollFD, i);
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int fd = pfd->fd;
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int revents = 0;
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if (FD_ISSET(fd, rfds)) {
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revents |= G_IO_IN | G_IO_HUP | G_IO_ERR;
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}
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if (FD_ISSET(fd, wfds)) {
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revents |= G_IO_OUT | G_IO_ERR;
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}
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if (FD_ISSET(fd, xfds)) {
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revents |= G_IO_PRI;
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}
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pfd->revents = revents & pfd->events;
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}
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}
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static int os_host_main_loop_wait(uint32_t timeout)
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{
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GMainContext *context = g_main_context_default();
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GPollFD poll_fds[1024 * 2]; /* this is probably overkill */
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int select_ret = 0;
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int g_poll_ret, ret, i, n_poll_fds;
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PollingEntry *pe;
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WaitObjects *w = &wait_objects;
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gint poll_timeout;
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static struct timeval tv0;
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fd_set rfds, wfds, xfds;
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int nfds;
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/* XXX: need to suppress polling by better using win32 events */
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ret = 0;
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for (pe = first_polling_entry; pe != NULL; pe = pe->next) {
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ret |= pe->func(pe->opaque);
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}
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if (ret != 0) {
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return ret;
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}
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g_main_context_prepare(context, &max_priority);
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n_poll_fds = g_main_context_query(context, max_priority, &poll_timeout,
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poll_fds, ARRAY_SIZE(poll_fds));
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g_assert(n_poll_fds <= ARRAY_SIZE(poll_fds));
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for (i = 0; i < w->num; i++) {
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poll_fds[n_poll_fds + i].fd = (DWORD_PTR)w->events[i];
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poll_fds[n_poll_fds + i].events = G_IO_IN;
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}
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if (poll_timeout < 0 || timeout < poll_timeout) {
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poll_timeout = timeout;
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}
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qemu_mutex_unlock_iothread();
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g_poll_ret = g_poll(poll_fds, n_poll_fds + w->num, poll_timeout);
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qemu_mutex_lock_iothread();
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if (g_poll_ret > 0) {
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for (i = 0; i < w->num; i++) {
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w->revents[i] = poll_fds[n_poll_fds + i].revents;
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}
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for (i = 0; i < w->num; i++) {
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if (w->revents[i] && w->func[i]) {
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w->func[i](w->opaque[i]);
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}
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}
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}
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if (g_main_context_check(context, max_priority, poll_fds, n_poll_fds)) {
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g_main_context_dispatch(context);
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}
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/* Call select after g_poll to avoid a useless iteration and therefore
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* improve socket latency.
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*/
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FD_ZERO(&rfds);
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FD_ZERO(&wfds);
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FD_ZERO(&xfds);
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nfds = pollfds_fill(gpollfds, &rfds, &wfds, &xfds);
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if (nfds >= 0) {
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select_ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv0);
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if (select_ret != 0) {
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timeout = 0;
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}
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if (select_ret > 0) {
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pollfds_poll(gpollfds, nfds, &rfds, &wfds, &xfds);
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}
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}
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return select_ret || g_poll_ret;
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}
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#endif
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int main_loop_wait(int nonblocking)
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{
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int ret;
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uint32_t timeout = UINT32_MAX;
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if (nonblocking) {
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timeout = 0;
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}
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/* poll any events */
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g_array_set_size(gpollfds, 0); /* reset for new iteration */
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/* XXX: separate device handlers from system ones */
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#ifdef CONFIG_SLIRP
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slirp_update_timeout(&timeout);
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slirp_pollfds_fill(gpollfds);
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#endif
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qemu_iohandler_fill(gpollfds);
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ret = os_host_main_loop_wait(timeout);
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qemu_iohandler_poll(gpollfds, ret);
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#ifdef CONFIG_SLIRP
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slirp_pollfds_poll(gpollfds, (ret < 0));
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#endif
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qemu_run_all_timers();
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return ret;
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}
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/* Functions to operate on the main QEMU AioContext. */
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QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque)
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{
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return aio_bh_new(qemu_aio_context, cb, opaque);
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}
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bool qemu_aio_wait(void)
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{
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return aio_poll(qemu_aio_context, true);
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}
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#ifdef CONFIG_POSIX
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void qemu_aio_set_fd_handler(int fd,
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IOHandler *io_read,
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IOHandler *io_write,
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AioFlushHandler *io_flush,
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void *opaque)
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{
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aio_set_fd_handler(qemu_aio_context, fd, io_read, io_write, io_flush,
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opaque);
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}
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#endif
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void qemu_aio_set_event_notifier(EventNotifier *notifier,
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EventNotifierHandler *io_read,
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AioFlushEventNotifierHandler *io_flush)
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{
|
|
aio_set_event_notifier(qemu_aio_context, notifier, io_read, io_flush);
|
|
}
|