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Message-ID: <3a72702f-6cf9-2b6e-0f9c-bf6857ab7ed2@tessares.net>
Date:   Wed, 30 Mar 2022 15:22:37 +0200
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Subject: Re: [PATCH] perf tools: Stop depending on .git files for building
 PERF-VERSION-FILE
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To:     John Garry <john.garry@huawei.com>, peterz@infradead.org,
        mingo@redhat.com, acme@kernel.org, mark.rutland@arm.com,
        alexander.shishkin@linux.intel.com, jolsa@kernel.org,
        namhyung@kernel.org, irogers@google.com
Cc:     linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
References: <1648635774-14581-1-git-send-email-john.garry@huawei.com>
From:   Matthieu Baerts <matthieu.baerts@tessares.net>
In-Reply-To: <1648635774-14581-1-git-send-email-john.garry@huawei.com>
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Hi John,

On 30/03/2022 12:22, John Garry wrote:
> This essentially reverts commit c72e3f04b45fb2e50cdd81a50c3778c6a57251d8
> and commit 4e666cdb06eede2069a7b1a96a1359d1c441a3eb.
> 
> In commit c72e3f04b45f ("tools/perf/build: Speed up git-version test on
> re-make"), a makefile dependency on .git/HEAD was added. The background is
> that running PERF-VERSION-FILE is relatively slow, and commands like
> "git describe" are particularly slow.
> 
> In commit 4e666cdb06ee ("perf tools: Fix dependency for version file
> creation"), an additional dependency on .git/ORIG_HEAD was added, as
> .git/HEAD may not change for "git reset --hard HEAD^" command. However,
> depending on whether we're on a branch or not, a "git cherry-pick" may
> not lead to the version being updated.
> 
> As discussed with the git community in [0], using git internal files for
> dependencies is not reliable. Commit 4e666cdb06ee also breaks some build
> scenarios [1].
> 
> As mentioned, c72e3f04b45f was added to speed up the build. However in
> commit 7572733b8499 ("perf tools: Fix version kernel tag") we removed the
> call to "git describe", so just revert Makefile.perf back to same as pre
> c72e3f04b45f and the build should not be so slow, as below:
> 
> Pre 7572733b8499:
> $> time util/PERF-VERSION-GEN
>   PERF_VERSION = 5.17.rc8.g4e666cdb06ee
> 
> real    0m0.110s
> user    0m0.091s
> sys     0m0.019s
> 
> Post 7572733b8499:
> $> time util/PERF-VERSION-GEN
>   PERF_VERSION = 5.17.rc8.g7572733b8499
> 
> real    0m0.039s
> user    0m0.036s
> sys     0m0.007s
> 
> [0] https://lore.kernel.org/git/87wngkpddp.fsf@igel.home/T/#m4a4dd6de52fdbe21179306cd57b3761eb07f45f8
> [1] https://lore.kernel.org/linux-perf-users/20220329093120.4173283-1-matthieu.baerts@tessares.net/T/#u
> 
> Fixes: 4e666cdb06ee ("perf tools: Fix dependency for version file creation")
> Reported-by: Matthieu Baerts <matthieu.baerts@tessares.net>
> Signed-off-by: John Garry <john.garry@huawei.com>

Thank you for your patch, I just tested it and it also fixes the issue I
reported!

Cheers,
Matt
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