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

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Date:	Thu, 21 Jun 2012 13:40:53 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	"Yan, Zheng" <zheng.z.yan@...el.com>, 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 Thu, 2012-06-21 at 11:13 +0200, Stephane Eranian wrote:

> >>> 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.
> >
> I was saying, I don't want to have to pass -C x with -a and yet have perf stat
> only instantiate the event once per socket. I think that's what PeterZ was
> asking about.

What Zheng is saying is that -a will iterate [0..nr_cpus), but since
we're interpreting the sys_perf_event_open(.cpu) argument as node, we'll
fail the syscall with -EINVAL or so for .cpu >= nr_node_ids.

This way, we'll only create one counter per node.

I would work, but its not pretty since we still don't know what we're
iterating.
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