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>
---
 iothread.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/iothread.c b/iothread.c
index 045825a348..14e9f3779e 100644
--- a/iothread.c
+++ b/iothread.c
@@ -64,6 +64,15 @@ 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);
 
         /*
-- 
2.17.1

On Wed, Mar 6, 2019 at 1:05 PM Peter Xu <peterx@redhat.com> wrote:
>
> 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>

> ---
>  iothread.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/iothread.c b/iothread.c
> index 045825a348..14e9f3779e 100644
> --- a/iothread.c
> +++ b/iothread.c
> @@ -64,6 +64,15 @@ 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);
>
>          /*
> --
> 2.17.1
>
>


-- 
Marc-André Lureau