linux-kernel - Re: git bisect and perf

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Message-ID: <CAL1RGDWjA8uh3924s4+F=zD3EJpUXk6auJpi=zPWJRE4sY8FCw@mail.gmail.com>
Date:	Tue, 5 Jun 2012 08:51:31 -0700
From:	Roland Dreier <roland@...estorage.com>
To:	David Ahern <dsahern@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: git bisect and perf

On Tue, Jun 5, 2012 at 8:29 AM, David Ahern <dsahern@...il.com> wrote:
> # git bisect good v2.6.38
> Some good revs are not ancestor of the bad rev.
> git bisect cannot work properly in this case.
> Maybe you mistake good and bad revs?

git bisect is telling you what is wrong -- as the man page says:

    This command uses git rev-list --bisect to help drive the binary
    search process to find which change introduced a bug, given an old
    "good" commit object name and a later "bad" commit object name.

so it assumes the good commit is older than the bad commit.

You can actually use git bisect in your case, although it gets very confusing
unless you write yourself a little wrapper alias: just swap the meaning of
good and bad, ie do

# git bisect start arch/x86/kernel/cpu/perf_event*
# git bisect good v2.6.35
# git bisect bad v2.6.38

and try somehow to remember that when you do a test, "bad" means
PEBS works and "good" means PEBS doesn't work.

 - R.
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