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Date: Sun, 12 May 2024 20:43:56 -0400
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Richard Gobert <richardbgobert@gmail.com>, 
 davem@davemloft.net, 
 edumazet@google.com, 
 kuba@kernel.org, 
 pabeni@redhat.com, 
 willemdebruijn.kernel@gmail.com, 
 dsahern@kernel.org, 
 alexander.duyck@gmail.com, 
 shuah@kernel.org, 
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 linux-kselftest@vger.kernel.org
Cc: Richard Gobert <richardbgobert@gmail.com>
Message-ID: <6641624c54b46_1d6c6729483@willemb.c.googlers.com.notmuch>
In-Reply-To: <20240509190819.2985-3-richardbgobert@gmail.com>
References: <20240509190819.2985-1-richardbgobert@gmail.com>
 <20240509190819.2985-3-richardbgobert@gmail.com>
Subject: Re: [PATCH net-next v10 2/3] net: gro: move L3 flush checks to
 tcp_gro_receive and udp_gro_receive_segment
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Richard Gobert 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 <richardbgobert@gmail.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>