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 18:47:44 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	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 6:39 PM, Maria Dimakopoulou
<maria.n.dimakopoulou@...il.com> wrote:
> 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.
>
I agree with Maria here. The reintegration is different problem.
The series here helps and is a required first step. Reintegration
will be added asap.

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