linux-kernel - Re: git bisect and perf

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Date:	Tue, 05 Jun 2012 11:12:03 -0600
From:	David Ahern <dsahern@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.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 10:05 AM, Peter Zijlstra wrote:
> On Tue, 2012-06-05 at 18:00 +0200, Peter Zijlstra wrote:
>> On Tue, 2012-06-05 at 09:29 -0600, David Ahern wrote:
>>> I am trying find out when (ie. which commit) the pebs feature
>>> actually
>>> started working on a westmere system
>>
>> What do you mean with working? The whole cycles:pp thing is magic and
>> unrelated to 'regular' PEBS stuff.

:p requires PEBS?

> .35 would indeed be the version we
>> introduced PEBS support and it should actually work.

I'm referring to cycles:p

model name	: Intel(R) Xeon(R) CPU           E5620  @ 2.40GHz
Fedora 14, 2.6.35.14-106.fc14.x86_64 (few perf_event* differences from 
2.6.35.14).

# perf record -e cycles:p -v -- sleep 1

   Warning:  ... trying to fall back to cpu-clock-ticks

...

Cycles is supported; it's the :p that is not. perf userspace only 
recently gained the knowledge for discriminating the two. Using perf 
from acme/perf/urgent:

# /tmp/pbuild/perf record -e cycles:p -v -- sleep 1

   Error: sys_perf_event_open() syscall returned with 28 (No space left 
on device).  /bin/dmesg may provide additional information.

I chased this to intel_pebs_constraints() returning &emptyconstraint 
which has a weight of 0 (validate_event -> intel_get_event_constraints 
-> intel_pebs_constraints).


>>
>> But if you're looking for the cycles:pp stuff (commit 7639dae0ca1)
>> that's .38-rc1-ish.
>
> So on kernels pre that commit you could still do:
>
>    perf record -e r108000c0:pp

Indeed that works on the F14 kernel.

David
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