linux-kernel - Re: [BUG] perf stat: explicit grouping yields unexpected results

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Message-ID: <CABPqkBRO=LNwHbRWKE_NnR5TUTh3sjTyp-9BOkvxQGKb2f3k7A@mail.gmail.com>
Date:	Fri, 15 Nov 2013 11:13:27 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>, "mingo@...e.hu" <mingo@...e.hu>,
	David Ahern <dsahern@...il.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung.kim@....com>
Subject: Re: [BUG] perf stat: explicit grouping yields unexpected results

On Fri, Nov 15, 2013 at 11:05 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Nov 15, 2013 at 07:34:57AM +0100, Ingo Molnar wrote:
>> Btw., does the kernel side currently support discovery of such
>> impossible group scheduling constraints at group setup time?
>
> Up to a point.
>
It is only looking at the group itself  not the overall condition
of the system, e.g., the other HT thread is case of shared
resources.
I think all it guarantees is that if the events in the group
are compatible with each other. And I think it covers the case
where the events use different counters but the same shared
resource, e.g., offcore_response on Intel X86.

>> If not
>> then it probably should and it should reject them straight away.
>
> We do I think, for the case where its obvious it can never fit.
>
> That said, if you have a pinned cpu event, it all comes apart.

You mean in the group?
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