linux-kernel - Re: [PATCH v2 02/11] perf/x86: Improve HT workaround GP counter constraint

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Date:	Wed, 27 May 2015 04:39:06 -0700
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Jiri Olsa <jolsa@...hat.com>,
	"Liang, Kan" <kan.liang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 02/11] perf/x86: Improve HT workaround GP counter constraint

On Wed, May 27, 2015 at 3:11 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, May 27, 2015 at 02:01:04AM -0700, Stephane Eranian wrote:
>> But are you removing the incremental calls from the upper layer via
>> x86_pmu.add()?
>> If not, then you are saying the dynamic constraint you got for
>> offcore_response, LBR
>> or the HT workaround is still the best avail now.
>
> sigh, see I knew I was missing something :/
>
> So then for c->flag & DYNAMIC we should put and get again, right?

I think it would still work. The constraint, even dynamic, you got on first
call is "locked" to you. So if you call x86_schedule_events multiple times
to add events like for E1, E2, E3 which causes at most 3 calls to
x86_schedule_events9). Then you'd get the same constraint but
it would still be valid. Just need to make sure you release it if scheduling
fails at event N and it has the dynamic constraint.
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