netdev - Re: [RFC PATCH] virtio-net: use NETIF_F_GRO_HW instead of NETIF_F

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Date:   Thu, 12 Aug 2021 00:50:03 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, ivan@...stigetransportation.com,
        xiangxia.m.yue@...il.com, willemb@...gle.com, edumazet@...gle.com
Subject: Re: [RFC PATCH] virtio-net: use NETIF_F_GRO_HW instead of NETIF_F_LRO

On Thu, Aug 12, 2021 at 11:23:04AM +0800, Jason Wang wrote:
> 
> 在 2021/8/12 上午6:17, Jakub Kicinski 写道:
> > On Wed, 11 Aug 2021 16:16:23 +0800 Jason Wang wrote:
> > > Try to fix this by using NETIF_F_GRO_HW instead so we're not
> > > guaranteed to be re-segmented as original.
> > This sentence may need rephrasing.
> 
> 
> Right, actually, I meant:
> 
> 
> Try to fix this by using NETIF_F_GRO_HW instead. But we're not sure the
> packet could be re-segmented to the exact original packet stream. Since it's
> really depends on the bakcend implementation.
> 
> 
> > 
> > > Or we may want a new netdev
> > > feature like RX_GSO since the guest offloads for virtio-net is
> > > actually to receive GSO packet.
> > > 
> > > Or we can try not advertise LRO is control guest offloads is not
> > > enabled. This solves the warning but will still slow down the traffic.
> > IMO gro-hw fits pretty well, patch looks good.
> 
> 
> If the re-segmentation is not a issue. I will post a formal patch.
> 
> Thanks


It is but the point is even though spec did not require this
we always allowed these configurations
in the past so hopefully most of them are not broken and combine
packets in the same way as GRO. Let's not break them all
in an attempt to catch bad configs, and meanwhile amend
the spec to recommend doing GW GRO.

> 
> >