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

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Message-ID: <AM0PR04MB47237705695AFD873DEE4530D49C9@AM0PR04MB4723.eurprd04.prod.outlook.com>
Date:   Mon, 17 Apr 2023 10:04:56 +0000
From:   Alvaro Karsz <alvaro.karsz@...id-run.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     Jason Wang <jasowang@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] virtio-net: reject small vring sizes

> > 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)
control vq even needs a bigger ring.

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