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It can be useful to run an AioContext from a thread which normally does
not "own" the AioContext. For example, request draining can be
implemented by acquiring the AioContext and looping aio_poll() until all
requests have been completed.
The following pattern should work:
/* Event loop thread */
while (running) {
aio_context_acquire(ctx);
aio_poll(ctx, true);
aio_context_release(ctx);
}
/* Another thread */
aio_context_acquire(ctx);
bdrv_read(bs, 0x1000, buf, 1);
aio_context_release(ctx);
This patch implements aio_context_acquire() and aio_context_release().
Note that existing aio_poll() callers do not need to worry about
acquiring and releasing - it is only needed when multiple threads will
call aio_poll() on the same AioContext.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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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>
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tests/test-aio.c used pipe2 which is Linux only. Use qemu_pipe
and qemu_set_nonblock for portabillity. Addition of O_CLOEXEC
is a harmless bonus.
Signed-off-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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sleep() apparently doesn't exist under mingw. Use g_usleep for
portability.
Signed-off-by: Alex Bligh <alex@alex.org.uk>
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
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Remove dummy_io_handler_flush from tests/test-aio.c as it does
nothing now.
Signed-off-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Add a test harness for AioContext timers. The g_source equivalent is
unsatisfactory as it suffers from false wakeups.
Signed-off-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Add a QEMUTimerListGroup each AioContext (meaning a QEMUTimerList
associated with each clock is added) and delete it when the
AioContext is freed.
Signed-off-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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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>
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Drop the io_flush argument to aio_set_event_notifier().
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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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>
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aio_poll(ctx, true) will soon block if any fd handlers have been set.
Previously it would only block when .io_flush() returned true.
This means that callers must check their wait condition *before*
aio_poll() to avoid deadlock.
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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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>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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There has been confusion between various aio wait and flush functions.
It's time to get rid of qemu_aio_flush() but in the aio test cases we
really do want this low-level functionality.
Therefore declare a local wait_for_aio() helper for the test cases.
Drop the aio_flush() test case.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
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