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From:   Alvaro Karsz <alvaro.karsz@solid-run.com>
To:     "Michael S. Tsirkin" <mst@redhat.com>
CC:     "jasowang@redhat.com" <jasowang@redhat.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
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        <virtualization@lists.linux-foundation.org>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "xuanzhuo@linux.alibaba.com" <xuanzhuo@linux.alibaba.com>
Subject: Re: [RFC PATCH net 0/3] virtio-net: allow usage of small vrings
Thread-Topic: [RFC PATCH net 0/3] virtio-net: allow usage of small vrings
Thread-Index: AQHZe2XUAgTluM5nJU6YPxcdS/aP2K9D4yuAgABAXH8=
Date:   Sun, 30 Apr 2023 18:15:03 +0000
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References: <20230430131518.2708471-1-alvaro.karsz@solid-run.com>
 <20230430100535-mutt-send-email-mst@kernel.org>
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=0A=
> > This patchset follows a discussion in the mailing list [1].=0A=
> >=0A=
> > This fixes only part of the bug, rings with less than 4 entries won't=
=0A=
> > work.=0A=
> =0A=
> Why the difference?=0A=
> =0A=
=0A=
Because the RING_SIZE < 4 case requires much more adjustments.=0A=
=0A=
* We may need to squeeze the virtio header into the headroom.=0A=
* We may need to squeeze the GSO header into the headroom, or block the fea=
tures.=0A=
* At the moment, without NETIF_F_SG, we can receive a skb with 2 segments, =
we may need to reduce it to 1.=0A=
* We may need to change all the control commands, so class,  command and co=
mmand specific data will fit in a single segment.=0A=
* We may need to disable the control command and all the features depending=
 on it.=0A=
* We may need to disable NAPI?=0A=
=0A=
There may be more changes..=0A=
=0A=
I was thinking that it may be easier to start with the easier case RING_SIZ=
E >=3D 4, make sure everything is working fine, then send a follow up patch=
set with the required adjustments for RING_SIZE < 4.=0A=