From: Peter Xu Date: Wed, 6 Mar 2019 11:55:32 +0000 (+0800) Subject: iothread: document about why we need explicit aio_poll() X-Git-Tag: v4.0.0-rc0~45^2 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6ca206204fa773c8626d59caf2a5676d6cc35f52;p=thirdparty%2Fqemu.git 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 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 --- diff --git a/iothread.c b/iothread.c index ad64c757ac3..7130be58e3e 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); /*