linux-kernel - Re: [PATCH 4/9] perf/x86: special case per-cpu core misc PMU events

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Date:	Fri, 17 Jul 2015 11:11:15 -0700
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mark Rutland <mark.rutland@....com>,
	"kan.liang@...el.com" <kan.liang@...el.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"acme@...nel.org" <acme@...nel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"adrian.hunter@...el.com" <adrian.hunter@...el.com>,
	"dsahern@...il.com" <dsahern@...il.com>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/9] perf/x86: special case per-cpu core misc PMU events

Hi,

On Fri, Jul 17, 2015 at 5:55 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Jul 17, 2015 at 01:21:06PM +0100, Mark Rutland wrote:
>>
>> As with my earlier comments, I don't think these can be grouped with
>> events (not even from the same PMU given their free-running nature).
>>
>> They're CPU-affine, so you can associate them with work done on that
>> CPU.
>
> Just record the deltas from them while you're on.

Yes, free-running are already handled by the kernel, the RAPL counters
are a good example.
The uncore IMC counters (for SNB/IVB/HSW/BDW) client processors is
another example.
Just compute deltas, and make sure you do not miss a wrap-around of
the counter if it is
not wide enough to never wrap-around.
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