aio-posix: ensure poll mode is left when aio_notify is called

aio-posix: ensure poll mode is left when aio_notify is called

With aio=thread, adaptive polling makes latency worse rather than
better, because it delays the execution of the ThreadPool's
completion bottom half.

event_notifier_poll() does run while polling, detecting that
a bottom half was scheduled by a worker thread, but because
ctx->notifier is explicitly ignored in run_poll_handlers_once(),
scheduling the BH does not count as making progress and
run_poll_handlers() keeps running.  Fix this by recomputing
the deadline after *timeout could have changed.

With this change, ThreadPool still cannot participate in polling
but at least it does not suffer from extra latency.

Reported-by: Sergio Lopez <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
Message-id: 20190409122823[email protected]
Cc: Stefan Hajnoczi <[email protected]>
Cc: Kevin Wolf <[email protected]>
Cc: [email protected]
Signed-off-by: Paolo Bonzini <[email protected]>
Message-Id: <1553692145[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
Message-Id: <20190409122823[email protected]>
Signed-off-by: Stefan Hajnoczi <[email protected]>