netdev - Re: [PATCH v2 net-next 0/3] gro: inline tcp6_gro

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Message-ID: <CANn89iJUh-3xDWkXhNatmBj2tWd1dLHXLbE6YT9EA2Lmb_yCLQ@mail.gmail.com>
Date: Tue, 20 Jan 2026 16:44:52 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: "David S . Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH v2 net-next 0/3] gro: inline tcp6_gro_{receive,complete}

On Tue, Jan 20, 2026 at 4:41 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Tue, Jan 20, 2026 at 4:30 PM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Sun, 18 Jan 2026 17:52:12 +0000 Eric Dumazet wrote:
> > > On some platforms, GRO stack is too deep and causes cpu stalls.
> > >
> > > Decreasing call depths by one shows a 1.5 % gain on Zen2 cpus.
> > > (32 RX queues, 100Gbit NIC, RFS enabled, tcp_rr with 128 threads and 10,000 flows)
> > >
> > > We can go further by inlining ipv6_gro_{receive,complete}
> > > and take care of IPv4 if there is interest.
> > >
> > > Note: two temporary __always_inline will be replaced with
> > >       inline_for_performance when available.
> > >
> > > v2: dealt with udp6_gro_receive()/udp6_gro_complete()
> > >     missing declarations (kernel test robot <lkp@...el.com>)
> > >     for CONFIG_MITIGATION_RETPOLINE=n
> >
> > Still not good?
> >
> > net/ipv6/udp_offload.c:136:17: error: static declaration of ‘udp6_gro_receive’ follows non-static declaration
> >   136 | struct sk_buff *udp6_gro_receive(struct list_head *head, struct sk_buff *skb)
> >       |                 ^~~~~~~~~~~~~~~~
> > In file included from net/ipv6/udp_offload.c:16:
> > ./include/net/gro.h:408:17: note: previous declaration of ‘udp6_gro_receive’ with type ‘struct sk_buff *(struct list_head *, struct sk_buff *)’
> >   408 | struct sk_buff *udp6_gro_receive(struct list_head *, struct sk_buff *);
> >       |                 ^~~~~~~~~~~~~~~~
> > net/ipv6/udp_offload.c:168:29: error: static declaration of ‘udp6_gro_complete’ follows non-static declaration
> >   168 | INDIRECT_CALLABLE_SCOPE int udp6_gro_complete(struct sk_buff *skb, int nhoff)
> >       |                             ^~~~~~~~~~~~~~~~~
> > ./include/net/gro.h:409:5: note: previous declaration of ‘udp6_gro_complete’ with type ‘int(struct sk_buff *, int)’
> >   409 | int udp6_gro_complete(struct sk_buff *, int);
> >       |     ^~~~~~~~~~~~~~~~~
>
> Oh well, I thought I tested this stuff.

Interesting... clang (our default compiler for kernel) does not complain at all.