netdev - Re: [net v4 2/3] net: sched: add check tc_skip

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Date:   Fri, 3 Dec 2021 22:35:34 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     xiangxia.m.yue@...il.com, netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, ast@...nel.org,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, edumazet@...gle.com,
        atenart@...nel.org, alexandr.lobakin@...el.com, weiwan@...gle.com,
        arnd@...db.de
Subject: Re: [net v4 2/3] net: sched: add check tc_skip_classify in sch egress

On 12/2/21 3:47 AM, xiangxia.m.yue@...il.com wrote:
> From: Tonghao Zhang <xiangxia.m.yue@...il.com>
> 
> Try to resolve the issues as below:
> * We look up and then check tc_skip_classify flag in net
>    sched layer, even though skb don't want to be classified.
>    That case may consume a lot of cpu cycles.
> 
>    Install the rules as below:
>    $ for id in $(seq 1 10000); do
>    $       tc filter add ... egress prio $id ... action mirred egress redirect dev ifb0
>    $ done
> 
>    netperf:
>    $ taskset -c 1 netperf -t TCP_RR -H ip -- -r 32,32
>    $ taskset -c 1 netperf -t TCP_STREAM -H ip -- -m 32
> 
>    Before: 152.04 tps, 0.58 Mbit/s
>    After:  303.07 tps, 1.51 Mbit/s
>    For TCP_RR, there are 99.3% improvement, TCP_STREAM 160.3%.

As it was pointed out earlier by Eric in v3, these numbers are moot since noone
is realistically running such a setup in practice with 10k linear rules.