linux-kernel - Re: perf version issues

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Date:   Tue, 22 Mar 2022 17:11:16 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     John Garry <john.garry@...wei.com>
Cc:     Ian Rogers <irogers@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: perf version issues

Re-adding lkml and Ian, Jiri, as I found some strange behaviour with
'git cherry-pick'.

Em Mon, Mar 21, 2022 at 08:43:26AM +0000, John Garry escreveu:
> Hi Arnaldo,
> 
> I have been finding that during my development that the output from "perf
> -v" may be incorrect in certain circumstances. I sent some patches to fix it
> up:
> https://lore.kernel.org/linux-perf-users/1645449409-158238-1-git-send-email-john.garry@huawei.com/T/#mf7234d2e331a53370c148eb4a0633d405a5c6832
> 
> Is there some issue that these cannot be processed?

So, while testing it I noticed that if we use 'git cherry-pick' it
doesn't trigger a rebuild, even having a new head :-\

I.e. with the two patches in at the HEAD, try:

  $ git log --oneline -2
  cb66befccba18fac (HEAD -> perf/core) perf tools: Fix version kernel tag
  4e666cdb06eede20 perf tools: Fix dependency for version file creation
  $ make -C tools/perf O=/tmp/build/perf install-bin
  $ perf -v
  perf version 5.17.rc8.gcb66befccba1

Ok so far, now lets remove HEAD and leave just the first patch, that has
the ORIG_HEAD dependency to trigger a rebuild:

  $ git reset --hard HEAD~
  HEAD is now at 4e666cdb06eede20 perf tools: Fix dependency for version file creation
  $ make -C tools/perf O=/tmp/build/perf install-bin
  $ perf -v
  perf version 5.17.rc8.g4e666cdb06ee

Ok, detected and rebuilt, perf -v works as expected.

Now lets try cherry picking your second patch:

$ git cherry-pick cb66befccba18fac
  [perf/core 8ff6a6c06a90a362] perf tools: Fix version kernel tag
   Author: John Garry <john.garry@...wei.com>
   Date: Mon Feb 21 21:16:49 2022 +0800
   1 file changed, 4 insertions(+), 9 deletions(-)
  $ make -C tools/perf O=/tmp/build/perf install-bin
  $ perf -v
  perf version 5.17.rc8.g4e666cdb06ee

Now it doesn´t notice it and there is no automatic rebuild triggered, we
stay with the cset from before the cherry-pick :-\

$ git log --oneline -2
8ff6a6c06a90a362 (HEAD -> perf/core) perf tools: Fix version kernel tag
4e666cdb06eede20 perf tools: Fix dependency for version file creation
$

Anyway, your patch works for some cases, so its an improvement and I'll
apply it, we can continue from there.

- Arnaldo