netdev - Re: [RFC PATCH net 2/3] virtio-net: allow usage of vrings smaller than MAX_SKB

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Message-ID: <AM0PR04MB4723AA2ABCE91928BE735DEBD46E9@AM0PR04MB4723.eurprd04.prod.outlook.com>
Date:   Mon, 1 May 2023 11:59:42 +0000
From:   Alvaro Karsz <alvaro.karsz@...id-run.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     "jasowang@...hat.com" <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>,
        "xuanzhuo@...ux.alibaba.com" <xuanzhuo@...ux.alibaba.com>
Subject: Re: [RFC PATCH net 2/3] virtio-net: allow usage of vrings smaller
 than MAX_SKB_FRAGS + 2

> First up to 4k should not be a problem. Even jumbo frames e.g. 9k
> is highly likely to succeed. And a probe time which is often boot
> even 64k isn't a problem ...
> 
> Hmm. We could allocate large buffers at probe time. Reuse them and
> copy data over.
> 
> IOW reusing  GOOD_COPY_LEN flow for this case.  Not yet sure how I feel
> about this. OTOH it removes the need for the whole feature blocking
> approach, does it not?
> WDYT?
> 

It could work..

In order to remove completely the feature blocking approach, we'll need to let the control commands fail (as you mentioned in the other patch).
I'm not sure I like it, it means many warnings from virtnet..
And it means accepting features that we know for sure that are not going to work.