netdev - Re: [PATCH v2] x86/csum: rewrite csum

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Date:   Fri, 12 Nov 2021 09:23:39 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>, x86@...nel.org,
        Alexander Duyck <alexander.duyck@...il.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: [PATCH v2] x86/csum: rewrite csum_partial()

On Fri, Nov 12, 2021 at 8:45 AM Peter Zijlstra <peterz@...radead.org> wrote:
>

>
> Looks nice, happen to have shiny perf numbers to show how awesome it it?
> :-)

On a networking load on cascadlake, line rate received on a single thread, I see
perf -e cycles:pp -C <cpu>

Before:
       4.16%  [kernel]       [k] csum_partial
After:
        0.83%  [kernel]       [k] csum_partial

If run in a loop 1,000,000 times,

Before:
       26,922,913      cycles                    # 3846130.429 GHz
        80,302,961      instructions              #    2.98  insn per
cycle
        21,059,816      branches                  # 3008545142.857
M/sec
             2,896      branch-misses             #    0.01% of all
branches
After:
        17,960,709      cycles                    # 3592141.800 GHz
        41,292,805      instructions              #    2.30  insn per
cycle
        11,058,119      branches                  # 2211623800.000
M/sec
             2,997      branch-misses             #    0.03% of all
branches

Thanks for your help !