netdev - Re: [net PATCH] skb: Do mix page pool and page referenced frags in GRO

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Date:   Sat, 28 Jan 2023 08:15:50 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Yunsheng Lin <linyunsheng@...wei.com>,
        Alexander Duyck <alexander.duyck@...il.com>, nbd@....name,
        davem@...emloft.net, hawk@...nel.org, ilias.apalodimas@...aro.org,
        linux-kernel@...r.kernel.org, lorenzo@...nel.org,
        netdev@...r.kernel.org, pabeni@...hat.com
Subject: Re: [net PATCH] skb: Do mix page pool and page referenced frags in GRO

On Sat, Jan 28, 2023 at 6:26 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Sat, 28 Jan 2023 10:37:47 +0800 Yunsheng Lin wrote:
> > If we are not allowing gro for the above case, setting NAPI_GRO_CB(p)->flush
> > to 1 in gro_list_prepare() seems to be making more sense so that the above
> > case has the same handling as skb_has_frag_list() handling?
> > https://elixir.bootlin.com/linux/v6.2-rc4/source/net/core/gro.c#L503
> >
> > As it seems to avoid some unnecessary operation according to comment
> > in tcp4_gro_receive():
> > https://elixir.bootlin.com/linux/v6.2-rc4/source/net/ipv4/tcp_offload.c#L322
>
> The frag_list case can be determined with just the input skb.
> For pp_recycle we need to compare input skb's pp_recycle with
> the pp_recycle of the skb already held by GRO.
>
> I'll hold off with applying a bit longer tho, in case Eric
> wants to chime in with an ack or opinion.

Doing the test only if the final step (once all headers have been
verified) seems less costly
for the vast majority of the cases the driver cooks skbs with a
consistent pp_recycle bit ?

So Alex patch seems less expensive to me than adding the check very early.