Subject: Re: [PATCH net-next v10 2/3] net: gro: move L3 flush checks to tcp_gro_receive and udp_gro_receive_segment

From: Jakub Kicinski <[email-masked]>
Date: Tue, 14 May 2024 07:14:07 -0700

On Tue, 14 May 2024 14:13:21 +0200 Geert Uytterhoeven wrote:
> On Thu, May 9, 2024 at 9:09 PM Richard Gobert <[email-masked]> wrote:
> > {inet,ipv6}_gro_receive functions perform flush checks (ttl, flags,
> > iph->id, ...) against all packets in a loop. These flush checks are used in
> > all merging UDP and TCP flows.
> >
> > These checks need to be done only once and only against the found p skb,
> > since they only affect flush and not same_flow.
> >
> > This patch leverages correct network header offsets from the cb for both
> > outer and inner network headers - allowing these checks to be done only
> > once, in tcp_gro_receive and udp_gro_receive_segment. As a result,
> > NAPI_GRO_CB(p)->flush is not used at all. In addition, flush_id checks are
> > more declarative and contained in inet_gro_flush, thus removing the need
> > for flush_id in napi_gro_cb.
> >
> > This results in less parsing code for non-loop flush tests for TCP and UDP
> > flows.
> >
> > To make sure results are not within noise range - I've made netfilter drop
> > all TCP packets, and measured CPU performance in GRO (in this case GRO is
> > responsible for about 50% of the CPU utilization).
> >
> > perf top while replaying 64 parallel IP/TCP streams merging in GRO:
> > (gro_receive_network_flush is compiled inline to tcp_gro_receive)
> > net-next:
> >         6.94% [kernel] [k] inet_gro_receive
> >         3.02% [kernel] [k] tcp_gro_receive
> >
> > patch applied:
> >         4.27% [kernel] [k] tcp_gro_receive
> >         4.22% [kernel] [k] inet_gro_receive
> >
> > perf top while replaying 64 parallel IP/IP/TCP streams merging in GRO (same
> > results for any encapsulation, in this case inet_gro_receive is top
> > offender in net-next)
> > net-next:
> >         10.09% [kernel] [k] inet_gro_receive
> >         2.08% [kernel] [k] tcp_gro_receive
> >
> > patch applied:
> >         6.97% [kernel] [k] inet_gro_receive
> >         3.68% [kernel] [k] tcp_gro_receive
> >
> > Signed-off-by: Richard Gobert <[email-masked]>  
> 
> Thanks for your patch, which is now commit 4b0ebbca3e167976 ("net: gro:
> move L3 flush checks to tcp_gro_receive and udp_gro_receive_segment")
> in net-next/main (next-20240514).
> 
> [email-masked] reports build failures on m68k, e.g.
> http://kisskb.ellerman.id.au/kisskb/buildresult/15168903/
> 
>     net/core/gro.c: In function ‘dev_gro_receive’:
>     ././include/linux/compiler_types.h:460:38: error: call to
> ‘__compiletime_assert_654’ declared with attribute error: BUILD_BUG_ON
> failed: !IS_ALIGNED(offsetof(struct napi_gro_cb, zeroed), sizeof(u32))

Hi Richard, any chance of getting this fixed within the next 2 hours?
I can't send the net-next PR if it doesn't build on one of the arches..