linux-kernel - Re: [PATCH V6 0/13] perf: Intel uncore pmu counting support

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Date:	Thu, 21 Jun 2012 16:43:06 +0800
From:	"Yan, Zheng" <zheng.z.yan@...el.com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, mingo@...e.hu,
	jolsa@...hat.com, andi@...stfloor.org,
	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH V6 0/13] perf: Intel uncore pmu counting support

On 06/21/2012 04:10 PM, Stephane Eranian wrote:
> On Thu, Jun 21, 2012 at 4:34 AM, Yan, Zheng <zheng.z.yan@...el.com> wrote:
>> On 06/21/2012 12:01 AM, Peter Zijlstra wrote:
>>>
>>> ok, so with this stuff something like:
>>>
>>>   perf stat -ae uncore/event=clockticks/ foo
>>>
>>> will register a counter per cpu, which is somewhat silly since we only
>>> need one per node. What would be the best way to 'fix' this?
>>>
>>> We could of course create another variant of -a which iterates nodes
>>> instead of cpus, -N or so.
>>>
>>> Alternatively we could try and describe this in sysfs in some way, one
>>> possibility would be to include a link to /sys/devices/system/{cpu,node}
>>> or somesuch and use that link to iterate the correct space.
>>>
>>> Any other suggestions?
>>>
>> How about treat the 'cpu' parameter for uncore event as socket id instead
>> of cpu id?
>>
> But that does not address the use case of Peter, i.e., no cpu parameter passed.
> Looks like sysfs might be the only way to do this in a portable manner.
> 
It does. For example, on a dual socket system, perf can only register uncore
counter with 'cpu' parameter is equal to 0 or 1. This method is hacky, but it
requires minimal change for the kernel and perf tool.

Regards
Yan, Zheng

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