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

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Message-ID: <20230417031052-mutt-send-email-mst@kernel.org>
Date:   Mon, 17 Apr 2023 03:11:38 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Alvaro Karsz <alvaro.karsz@...id-run.com>
Cc:     Xuan Zhuo <xuanzhuo@...ux.alibaba.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>,
        Jason Wang <jasowang@...hat.com>
Subject: Re: [PATCH net] virtio-net: reject small vring sizes

On Mon, Apr 17, 2023 at 07:07:59AM +0000, Alvaro Karsz wrote:
> > Why tx timeout without frags?
> 
> Please see my response to Michael.
> 
> > > * Guest GSO/big MTU (without VIRTIO_NET_F_MRG_RXBUF?), we can't chain page size buffers anymore.
> > 
> > 
> > Or, we disable the GUEST_GSO, HOST_GSO......
> > 
> And disable VIRTIO_NET_F_MTU, quoting the spec:
> "A driver SHOULD negotiate VIRTIO_NET_F_MTU if the device offers it."

If you don't the nic can still get jumbo packets it will just drop them ...

> We can find a way around using buffers bigger than a page size like Michael implied.