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

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Message-ID: <20150527140051.GS19417@two.firstfloor.org>
Date:	Wed, 27 May 2015 16:00:52 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>, mingo@...nel.org,
	vincent.weaver@...ne.edu, eranian@...gle.com, jolsa@...hat.com,
	kan.liang@...el.com, 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 09:48:09AM +0200, Peter Zijlstra wrote:
> On Tue, May 26, 2015 at 04:33:42PM -0700, Andi Kleen wrote:
> > Peter Zijlstra <peterz@...radead.org> writes:
> > > +		 */
> > > +		if (is_ht_workaround_enabled() && !cpuc->is_fake &&
> > 
> > Could this function also check if at least one leaking event is
> > scheduled somewhere? (e.g. from a global count)
> 
> You truncated one line too many:
> 
> +               if (is_ht_workaround_enabled() && !cpuc->is_fake &&
> +                   READ_ONCE(cpuc->excl_cntrs->exclusive_present))
> +                       gpmax /= 2;
> 
> Guess what that READ_ONCE() does? It checks if there's one such leaky
> event on the current core.

Great. Thanks.

-Andi


-- 
ak@...ux.intel.com -- Speaking for myself only.
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