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 <ch...@gentoo.org> Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com> --- util/async.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/util/async.c b/util/async.c index 4e4c7af51e..ca83e32c7f 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); } } -- 2.23.0
