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

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Date:	Thu, 5 Jun 2014 19:39:55 +0300
From:	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
To:	Borislav Petkov <bp@...en8.de>
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 5, 2014 at 6:17 PM, Borislav Petkov <bp@...en8.de> wrote:
> 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...
>

This series aims to avoid corruption of non-corrupting events.
Re-integration of the counts is not related to this. This is why
we chose to fix this other problem on a second series to keep
things clean and concepts separated.

> --
> Regards/Gruss,
>     Boris.
>
> Sent from a fat crate under my desk. Formatting is fine.
> --
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