iothread: document about why we need explicit aio_poll()

After consulting Paolo I know why we'd better keep the explicit
aio_poll() in iothread_run().  Document it directly into the code so
that future readers will know the answer from day one.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20190306115532.23025-6-peterx@redhat.com
Message-Id: <20190306115532.23025-6-peterx@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Peter Xu 2019-03-06 19:55:32 +08:00 committed by Stefan Hajnoczi
parent b60ec76a13
commit 6ca206204f

View file

@ -63,6 +63,15 @@ static void *iothread_run(void *opaque)
qemu_sem_post(&iothread->init_done_sem);
while (iothread->running) {
/*
* Note: from functional-wise the g_main_loop_run() below can
* already cover the aio_poll() events, but we can't run the
* main loop unconditionally because explicit aio_poll() here
* is faster than g_main_loop_run() when we do not need the
* gcontext at all (e.g., pure block layer iothreads). In
* other words, when we want to run the gcontext with the
* iothread we need to pay some performance for functionality.
*/
aio_poll(iothread->ctx, true);
/*