linux-kernel - Re: git bisect and perf

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Message-ID: <4FCE3A56.9060400@gmail.com>
Date:	Tue, 05 Jun 2012 10:56:54 -0600
From:	David Ahern <dsahern@...il.com>
To:	Roland Dreier <roland@...estorage.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 6/5/12 9:51 AM, Roland Dreier wrote:
> 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.

Thanks, Roland. I'll reverse the logic.

David
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