linux-kernel - Re: [PATCH 9/9] perf/x86: add syfs entry to disable HT bug workaround

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Message-ID: <20140605151734.GD16811@pd.tnic>
Date:	Thu, 5 Jun 2014 17:17:34 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
Cc:	Stephane Eranian <eranian@...gle.com>,
	Matt Fleming <matt@...sole-pimps.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Jiri Olsa <jolsa@...hat.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>
Subject: Re: [PATCH 9/9] perf/x86: add syfs entry to disable HT bug workaround

On Thu, Jun 05, 2014 at 05:45:24PM +0300, Maria Dimakopoulou wrote:
> The issue is that the outcoming leaked counts are not compensated
> by the incoming leaked counts of the sibling thread. With the workaround,
> corrupting events are always scheduled with an empty sibling counter.
> This means that their leaked counts are lost. So it is expected to see
> lower counts with the workaround. Note that this is not a side-effect of
> the workaround; leaked counts are expected to be lost with nothing
> measured on the sibling counter in general.
> 
> In a second series we intend to re-integrate the counts for counting mode
> events. The workaround makes this easier because it guarantees
> that the sibling counter is unused, thus its counts are purely leaked
> counts and they can be safely re-integrated.

IIUC, sounds to me like reintegrating the leaked counts from the unused
counter should be part of the workaround too, not a second series...

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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