From 6ca206204fa773c8626d59caf2a5676d6cc35f52 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Wed, 6 Mar 2019 19:55:32 +0800 Subject: [PATCH] iothread: document about why we need explicit aio_poll() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Marc-André Lureau Message-id: 20190306115532.23025-6-peterx@redhat.com Message-Id: <20190306115532.23025-6-peterx@redhat.com> Signed-off-by: Stefan Hajnoczi --- iothread.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/iothread.c b/iothread.c index ad64c757ac..7130be58e3 100644 --- a/iothread.c +++ b/iothread.c @@ -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); /*