diff options
| author | Marc-André Lureau <marcandre.lureau@redhat.com> | 2019-10-01 17:26:09 +0400 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2019-10-04 18:49:18 +0200 |
| commit | 873df2cec13138718466fc5f68d801971390542b (patch) | |
| tree | 55c39e65a9b0b24c79ae25a1d650c2b3cd6d9482 /util | |
| parent | 2d18ec29ba455a150f29aa5ac4d21b0ebdc5cd4d (diff) | |
| download | qemu-873df2cec13138718466fc5f68d801971390542b.zip qemu-873df2cec13138718466fc5f68d801971390542b.tar.gz qemu-873df2cec13138718466fc5f68d801971390542b.tar.bz2 | |
win32: work around main-loop busy loop on socket/fd event
Commit 05e514b1d4d5bd4209e2c8bbc76ff05c85a235f3 introduced an AIO
context optimization to avoid calling event_notifier_test_and_clear() on
ctx->notifier. On Windows, the same notifier is being used to wakeup the
wait on socket events (see commit
d3385eb448e38f828c78f8f68ec5d79c66a58b5d).
The ctx->notifier event is added to the gpoll sources in
aio_set_event_notifier(), aio_ctx_check() should clear the event
regardless of ctx->notified, since Windows sets the event by itself,
bypassing the aio->notified. This fixes qemu not clearing the event
resulting in a busy loop.
Paolo suggested to me on irc to call event_notifier_test_and_clear()
after select() >0 from aio-win32.c's aio_prepare. Unfortunately, not all
fds associated with ctx->notifiers are in AIO fd handlers set.
(qemu_set_nonblock() in util/oslib-win32.c calls qemu_fd_register()).
This is essentially a v2 of a patch that was sent earlier:
https://lists.gnu.org/archive/html/qemu-devel/2017-01/msg00420.html
that resurfaced when James investigated Spice performance issues on Windows:
https://gitlab.freedesktop.org/spice/spice/issues/36
In order to test that patch, I simply tried running test-char on
win32, and it hangs. Applying that patch solves it. QIO idle sources
are not dispatched. I haven't investigated much further, I suspect
source priorities and busy looping still come into play.
This version keeps the "notified" field, so event_notifier_poll()
should still work as expected.
Cc: James Le Cuirot <chewi@gentoo.org>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'util')
| -rw-r--r-- | util/async.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/util/async.c b/util/async.c index 4e4c7af..ca83e32 100644 --- a/util/async.c +++ b/util/async.c @@ -354,7 +354,11 @@ void aio_notify(AioContext *ctx) void aio_notify_accept(AioContext *ctx) { - if (atomic_xchg(&ctx->notified, false)) { + if (atomic_xchg(&ctx->notified, false) +#ifdef WIN32 + || true +#endif + ) { event_notifier_test_and_clear(&ctx->notifier); } } |