Re: [virtio-dev] Re: [PATCH v6] virtio-snd: add virtio sound device specification

[Anton Yakovlev <anton.yakovlev@opensynergy.com>]

On 03.03.2020 13:10, Gerd Hoffmann wrote:
> On Tue, Mar 03, 2020 at 12:28:32PM +0100, Anton Yakovlev wrote:
> > Hi,
> >
> > On 03.03.2020 12:20, Gerd Hoffmann wrote:
> > >     Hi,
> > >
> > > > 4. Introduce the polling mode feature for a message-based transport.
> > >
> > > BTW: is that driver -> device or device -> driver or both?
> > > In case both: should we have two separate feature flags maybe?
> >
> > It's driver -> device direction. The driver needs notifications from the
> > device in any case, so it makes no sense to suppress notifications in this
> > direction (device -> driver).
>
> Hmm, unless I missed something it doesn't matter whenever the guest
> kernel checks virtqueues from irq handler or timer ...

Because in the general case, it is impossible to predict when a notification
will come from the device. Even if we are talking about a period time, this
does not mean that the device will send notifications precisely at these
intervals. And this means that the driver must do a tricky poll, trying
to guess when the notification will arrive, i.e. just waste CPU resources.


> cheers,
>    Gerd

--
Anton Yakovlev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin