linux-kernel - Re: [PATCH net-next v3 0/3] make skip

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Date: Mon, 11 Mar 2024 22:05:28 +0000
From: Asbjørn Sloth Tønnesen <ast@...erby.net>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang
 <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
 Daniel Borkmann <daniel@...earbox.net>, Vlad Buslov <vladbu@...dia.com>,
 Marcelo Ricardo Leitner <mleitner@...hat.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, llu@...erby.dk
Subject: Re: [PATCH net-next v3 0/3] make skip_sw actually skip software

Hi Kuba,

On 3/11/24 8:44 PM, Jakub Kicinski wrote:
> On Wed,  6 Mar 2024 16:58:08 +0000 Asbjørn Sloth Tønnesen wrote:
>> During development of flower-route[1], which I
>> recently presented at FOSDEM[2], I noticed that
>> CPU usage, would increase the more rules I installed
>> into the hardware for IP forwarding offloading.
>>
>> Since we use TC flower offload for the hottest
>> prefixes, and leave the long tail to the normal (non-TC)
>> Linux network stack for slow-path IP forwarding.
>> We therefore need both the hardware and software
>> datapath to perform well.
>>
>> I found that skip_sw rules, are quite expensive
>> in the kernel datapath, since they must be evaluated
>> and matched upon, before the kernel checks the
>> skip_sw flag.
>>
>> This patchset optimizes the case where all rules
>> are skip_sw, by implementing a TC bypass for these
>> cases, where TC is only used as a control plane
>> for the hardware path.
> 
> Linus tagged v6.8 and the merge window for v6.9 has started.
> This feels a bit too risky for me to apply last minute,
> could you repost in 2 weeks once the merge window is over?

Sure, I will repost once net-next opens back up again.

-- 
Best regards
Asbjørn Sloth Tønnesen
Network Engineer
Fiberby - AS42541