Re: [PATCH v8 03/12] virtio-sound: handle control messages and streams

[Philippe Mathieu-Daudé]

On 4/9/23 12:18, Manos Pitsidianakis wrote:
> Good morning Philippe,
>
> On Mon, 04 Sep 2023 13:08, Philippe Mathieu-Daudé <philmd@linaro.org> 
> wrote:
> > > +    iov_from_buf(cmd->elem->in_sg,
> > > +                 cmd->elem->in_num,
> > > +                 0,
> > > +                 &cmd->resp,
> > > +                 sizeof(cmd->resp));
> > > +    virtqueue_push(cmd->vq, cmd->elem, sizeof(cmd->elem));
> > > +    virtio_notify(VIRTIO_DEVICE(s), cmd->vq);
> >
> > I have very few understanding of virtio, but I'm wondering here,
> > since this function is called under cmdq_mutex(), could it be
> > useful to batch the queue by calling virtio_notify() only once
> > in the caller once the whole cmdq is processed ...
>
> In the linux driver (sound/virtio/virtio_ctl_msg.c), the guest has a 
> timeout for receiving the message. I found that if I did not notify as 
> fast as possible, I got timeout errors on the guest.

Ah, I see, 1ms per default:

sound/virtio/virtio_card.c:14:u32 virtsnd_msg_timeout_ms = MSEC_PER_SEC;