Re: [Qemu-devel] [PATCH v3 09/10] aio: add .io_poll_begin/end() callbacks

[Paolo Bonzini <pbonzini@redhat.com>]

On 22/11/2016 17:31, Stefan Hajnoczi wrote:
> +static bool try_poll_mode(AioContext *ctx, bool enable)
> +{
> +    if (enable && aio_poll_max_ns && ctx->poll_disable_cnt == 0) {
> +        /* See qemu_soonest_timeout() uint64_t hack */
> +        int64_t max_ns = MIN((uint64_t)aio_compute_timeout(ctx),
> +                             (uint64_t)aio_poll_max_ns);
> +
> +        if (max_ns) {
> +            poll_set_started(ctx, true);
> +
> +            if (run_poll_handlers(ctx, max_ns)) {
> +                return true;
> +            }
> +        }
> +    }
> +
> +    poll_set_started(ctx, false);

You could do a single iteration even if enable == false (which I'd
rename to blocking, BTW, because poll_start can be false on exit even if
enable == true).

In fact, since (like virtio_queue_host_notifier_aio_poll_end) all
.io_poll_end() callbacks are going to poll once more, what about adding
here:

    return run_poll_handlers(ctx, 0);

or just an instance of the loop, without qemu_clock_get_ns and the
tracepoints:

    return run_poll_handlers_once(ctx);

and removing from patch 10 the

    /* Handle any buffers that snuck in after we finished polling */
    virtio_queue_host_notifier_aio_poll(n);

?

Thanks,

Paolo