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

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

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>