linux-kernel - Re: [PATCH 02/10] perf/x86: Improve HT workaround GP counter constraint

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Message-ID: <20150522133636.GE3644@twins.programming.kicks-ass.net>
Date:	Fri, 22 May 2015 15:36:36 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/10] perf/x86: Improve HT workaround GP counter
 constraint

On Fri, May 22, 2015 at 06:29:47AM -0700, Stephane Eranian wrote:
> On Fri, May 22, 2015 at 6:25 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Fri, May 22, 2015 at 06:07:00AM -0700, Stephane Eranian wrote:
> >>
> >> One other thing I noticed is that the --n_excl needs to be protected by the
> >> excl_cntrs->lock in put_excl_constraints().
> >
> > Nah, its strictly per cpu.
> 
> No. the excl_cntrs struct is pointed to by cpuc but it is shared between the
> sibling HT. Otherwise this would not work!

n_excl is per cpuc, see the trickery with has_exclusive vs
exclusive_present on how I avoid the lock.
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