Re: [PATCH net] virtio-net: reject small vring sizes

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Alvaro Karsz <alvaro.karsz@solid-run.com>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"virtualization@lists.linux-foundation.org"
	<virtualization@lists.linux-foundation.org>,
	"edumazet@google.com" <edumazet@google.com>,
	"kuba@kernel.org" <kuba@kernel.org>,
	"pabeni@redhat.com" <pabeni@redhat.com>,
	"davem@davemloft.net" <davem@davemloft.net>
Subject: Re: [PATCH net] virtio-net: reject small vring sizes
Date: Mon, 17 Apr 2023 07:40:19 -0400	[thread overview]
Message-ID: <20230417073830-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <AM0PR04MB47237705695AFD873DEE4530D49C9@AM0PR04MB4723.eurprd04.prod.outlook.com>

On Mon, Apr 17, 2023 at 10:04:56AM +0000, Alvaro Karsz wrote:
> > > So, what do you think, we should fix virtio-net to work with smaller rings? we should fail probe?
> > >
> > > I think that since this never came up until now, there is no big demand to such small rings.
> > 
> > The worry is that once we start failing probe there's just a tiny chance
> > hosts begin to rely on us failing probe then we won't be able to fix it.
> > So it depends on the size of the patch I think. So far it seems small enough
> > that wasting code on failing probe isn't worth it.
> > 
> 
> I see your point.
> Regardless, we'll need to fail probe in some cases.
> ring size of 1 for example (if I'm not mistaken)

Hmm. We can make it work if we increase hard header size, then
there will always be room for vnet header.

> control vq even needs a bigger ring.

Why does it?

> Maybe we can fix virtnet to allow smaller rings + fail probe in some cases, all in the same patch/patchset.

If we can't make it work then yes.

-- 
MST

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