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From:   Alvaro Karsz <alvaro.karsz@solid-run.com>
To:     "Michael S. Tsirkin" <mst@redhat.com>
CC:     Jason Wang <jasowang@redhat.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "edumazet@google.com" <edumazet@google.com>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "pabeni@redhat.com" <pabeni@redhat.com>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net] virtio-net: reject small vring sizes
Thread-Topic: [PATCH net] virtio-net: reject small vring sizes
Thread-Index: AQHZcDeGnH5xR2OGlkuo4s6jvhNMC68uIjT9gABGFgCAAG90AIAAMSwAgAABjzCAAARBAIAABATIgAAENICAAAM4M4AAIQOAgAALfyGAABuqgIAAAQKH
Date:   Mon, 17 Apr 2023 11:51:22 +0000
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> > I see your point.=0A=
> > Regardless, we'll need to fail probe in some cases.=0A=
> > ring size of 1 for example (if I'm not mistaken)=0A=
> =0A=
> Hmm. We can make it work if we increase hard header size, then=0A=
> there will always be room for vnet header.=0A=
> =0A=
> > control vq even needs a bigger ring.=0A=
> =0A=
> Why does it?=0A=
=0A=
At the moment, most of the commands chain 3 descriptors:=0A=
1 - class + command=0A=
2 - command specific=0A=
3 - ack=0A=
=0A=
We could merge 1 and 2 into a single one, both are read only for the device=
, so I take it back, it won't need a bigger ring.=0A=
But it will need 2 descriptors at least(1 read only for the device and 1 wr=
ite only for the device), so we still need to fail probe sometimes.=0A=