[virtio-dev] RE: [virtio-comment] RE: [PATCH v13] virtio-net: support the virtqueue coalescing moderation

From: Parav Pandit <parav@nvidia.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Cornelia Huck <cohuck@redhat.com>,
	Heng Qi <hengqi@linux.alibaba.com>,
	"virtio-dev@lists.oasis-open.org"
	<virtio-dev@lists.oasis-open.org>,
	"virtio-comment@lists.oasis-open.org"
	<virtio-comment@lists.oasis-open.org>,
	Jason Wang <jasowang@redhat.com>,
	Alvaro Karsz <alvaro.karsz@solid-run.com>,
	David Edmondson <david.edmondson@oracle.com>,
	Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Subject: [virtio-dev] RE: [virtio-comment] RE: [PATCH v13] virtio-net: support the virtqueue coalescing moderation
Date: Wed, 22 Mar 2023 17:02:52 +0000	[thread overview]
Message-ID: <PH0PR12MB5481B513EF0CAD4020A4C246DC869@PH0PR12MB5481.namprd12.prod.outlook.com> (raw)
In-Reply-To: <20230322125058-mutt-send-email-mst@kernel.org>

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Wednesday, March 22, 2023 12:53 PM
> 
> On Wed, Mar 22, 2023 at 04:49:58PM +0000, Parav Pandit wrote:
> >
> > > From: Michael S. Tsirkin <mst@redhat.com>
> > > Sent: Wednesday, March 22, 2023 12:47 PM
> > >
> > > I agree with Cornelia here. Yes if devices do not want to trust
> > > drivers then they will validate input but what exactly happens then is
> currently up to device.
> > > If we want to try and specify devices in all cases of out of spec
> > > input that's a big project, certainly doable but I would rather not
> > > connect it to this, rather boutique, feature.
> > Both of your and Cornelia's comment is abstract to me.
> > We cannot change past.
> 
> But we can make sure things are consistent. Currently we don't describe device
> behaviour if driver is out of spec and I see 0 reasons to start doing it with
> coalescing commands specifically.
> 
> > For the new command of interest here, hen driver supplied incorrect values,
> the device will return error.
> 
> It might be easier for device to just set NEEDS_RESET and stop responding. 
This approach of treating all errors as a fatal category is completely the opposite of making the device and driver resilient to (recoverable) errors.
We shouldn't go this route.
Different discussion...

> For
> a hypervisor implementation that's often better than returning error since
> device state is then preserved making things easier to debug.
> 
> > How to implement is upto the device to figure out.
> 
> 
> what to do is also up to the device.
Previously error code as not returned hence new command cannot return the error code is going backward.

Returning the failure code is a way to indicate that the driver had a recoverable error.

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