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From:   Junio C Hamano <gitster@pobox.com>
To:     Christian Couder <christian.couder@gmail.com>
Cc:     ZheNing Hu via GitGitGadget <gitgitgadget@gmail.com>,
        git <git@vger.kernel.org>, Hariom Verma <hariom18599@gmail.com>,
        Bagas Sanjaya <bagasdotme@gmail.com>,
        Jeff King <peff@peff.net>,
        =?utf-8?B?w4Z2YXIgQXJuZmrDtnLDsA==?= Bjarmason <avarab@gmail.com>,
        Eric Sunshine <sunshine@sunshineco.com>,
        ZheNing Hu <adlternative@gmail.com>
Subject: Re: [PATCH 14/19] [GSOC] cat-file: reuse ref-filter logic
References: <pull.993.git.1626090419.gitgitgadget@gmail.com>
        <70e83e4ba3cc8a55bb8d90cb2c581cd04ac116d4.1626090419.git.gitgitgadget@gmail.com>
        <CAP8UFD0vHw8cK90RbOUcrAcxNKiHVTMX0VEiK8+MNyHH0CNm4A@mail.gmail.com>
Date:   Mon, 12 Jul 2021 13:38:31 -0700
In-Reply-To: <CAP8UFD0vHw8cK90RbOUcrAcxNKiHVTMX0VEiK8+MNyHH0CNm4A@mail.gmail.com>
        (Christian Couder's message of "Mon, 12 Jul 2021 15:17:33 +0200")
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Christian Couder <christian.couder@gmail.com> writes:

>> The performance for `git cat-file --batch-all-objects --batch
>> >/dev/null` on the Git repository itself with performance testing
>> tool `time` change from "27.37s user 0.29s system 98% cpu 28.089
>> total" to "33.69s user 1.54s system 87% cpu 40.258 total".
>
> Saying that a later patch will add a fast path which will mitigate the
> performance regression introduced by this patch might help reassure
> reviewers.

More importantly, why is such a fast-path even needed?  Isn't it a
sign that the ref-filter implementation is eating more cycles than
it should for given set of placeholders?  Do we know where the extra
cycles goes?

I find it somewhat alarming if we are talking about "fast-path"
workaround before understanding why we are seeing slowdown in the
first place.