Re: git bisect and perf

[Stephane Eranian]

On Tue, Jun 5, 2012 at 7:12 PM, David Ahern <dsahern@xxxxxxxxx> wrote:
> 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   Â: Intel(R) Xeon(R) CPU      E5620 Â@ 2.40GHz
That's not as helpful as /proc/cpuinfo. I suspect this is a Westmere
system, isn't it?

> 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
>
> ÂWarning: Â... 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
>
> ÂError: sys_perf_event_open() syscall returned with 28 (No space left on
> device). Â/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:
>>
>> Â perf record -e r108000c0:pp
>
>
> Indeed that works on the F14 kernel.
>
> David
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