This patch drops a special case where aio_poll(ctx, true) returns false
instead of blocking if no file descriptors are waiting on I/O. Now it
is possible to block in aio_poll() to wait for aio_notify().
This change eliminates busy waiting. bdrv_drain_all() used to rely on
busy waiting to completed throttled I/O requests but this is no longer
required so we can simplify aio_poll().
Note that aio_poll() still returns false when aio_notify() was used. In
other words, stopping a blocking aio_poll() wait is not considered
making progress.
Adjust test-aio /aio/bh/callback-delete/one which assumed aio_poll(ctx,
true) would immediately return false instead of blocking.
Reviewed-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
The AioHandler->opaque field does not exist in aio-win32.c. The code
that uses it was incorrectly copied from aio-posix.c. For Windows we
can use AioHandler->e to match against AioContext->notifier.
This patch fixes the Windows build for aio-win32.o.
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Convert aio_poll to use deadline based on AioContext's timers.
aio_poll has been changed to return accurately whether progress
has occurred. Prior to this commit, aio_poll always returned
true if g_poll was entered, whether or not any progress was
made. This required a change to tests/test-aio.c where an
assert was backwards.
Signed-off-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
The .io_flush() handler no longer exists and has no users. Drop the
io_flush argument to aio_set_fd_handler() and related functions.
The AioFlushEventNotifierHandler and AioFlushHandler typedefs are no
longer used and are dropped too.
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Now that aio_poll() users check their termination condition themselves,
it is no longer necessary to call .io_flush() handlers.
The behavior of aio_poll() changes as follows:
1. .io_flush() is no longer invoked and file descriptors are *always*
monitored. Previously returning 0 from .io_flush() would skip this file
descriptor.
Due to this change it is essential to check that requests are pending
before calling qemu_aio_wait(). Failure to do so means we block, for
example, waiting for an idle iSCSI socket to become readable when there
are no requests. Currently all qemu_aio_wait()/aio_poll() callers check
before calling.
2. aio_poll() now returns true if progress was made (BH or fd handlers
executed) and false otherwise. Previously it would return true whenever
'busy', which means that .io_flush() returned true. The 'busy' concept
no longer exists so just progress is returned.
Due to this change we need to update tests/test-aio.c which asserts
aio_poll() return values. Note that QEMU doesn't actually rely on these
return values so only tests/test-aio.c cares.
Note that ctx->notifier, the EventNotifier fd used for aio_notify(), is
now handled as a special case. This is a little ugly but maintains
aio_poll() semantics, i.e. aio_notify() does not count as 'progress' and
aio_poll() avoids blocking when the user has not set any fd handlers yet.
Patches after this remove .io_flush() handler code until we can finally
drop the io_flush arguments to aio_set_fd_handler() and friends.
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
aio_poll() must return true if any work is still pending, even if it
didn't make progress, so that bdrv_drain_all() doesn't stop waiting too
early. The possibility of stopping early occasionally lead to a failed
assertion in bdrv_drain_all(), when some in-flight request was missed
and the function didn't really drain all requests.
In order to make that change, the return value as specified in the
function comment must change for blocking = false; fortunately, the
return value of blocking = false callers is only used in test cases, so
this change shouldn't cause any trouble.
Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
The repeated calls to WaitForMultipleObjects may cause a livelock in aio_poll,
where no progress is made on bottom halves. This patch matches the behavior
of the POSIX code.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
In the current code, this is done by qemu_set_fd_handler2, which is
called by qemu_aio_set_fd_handler. We need to keep the same behavior
even after removing the call to qemu_set_fd_handler2.
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The Win32 implementation will only accept EventNotifiers, thus a few
drivers are disabled under Windows. EventNotifiers are a good match
for the GSource implementation, too, because the Win32 port of glib
allows to place their HANDLEs in a GPollFD.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
