linux-kernel - Re: [PATCH 5/9] perf/x86: implement cross-HT corruption bug workaround

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Date:	Thu, 5 Jun 2014 16:15:17 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.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>,
	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
Subject: Re: [PATCH 5/9] perf/x86: implement cross-HT corruption bug workaround

On Thu, Jun 5, 2014 at 4:04 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Jun 04, 2014 at 11:34:14PM +0200, Stephane Eranian wrote:
>> +
>> +     /*
>> +      * Modify static constraint with current dynamic
>> +      * state of thread
>> +      *
>> +      * EXCLUSIVE: sibling counter measuring exclusive event
>> +      * SHARED   : sibling counter measuring non-exclusive event
>> +      * UNUSED   : sibling counter unused
>> +      */
>> +     for_each_set_bit(i, cx->idxmsk, X86_PMC_IDX_MAX) {
>> +             /*
>> +              * exclusive event in sibling counter
>> +              * our corresponding counter cannot be used
>> +              * regardless of our event
>> +              */
>> +             if (xl->state[i] == INTEL_EXCL_EXCLUSIVE)
>> +                     __clear_bit(i, cx->idxmsk);
>> +             /*
>> +              * if measuring an exclusive event, sibling
>> +              * measuring non-exclusive, then counter cannot
>> +              * be used
>> +              */
>> +             if (is_excl && xl->state[i] == INTEL_EXCL_SHARED)
>> +                     __clear_bit(i, cx->idxmsk);
>> +     }
>> +
>> +     /*
>> +      * recompute actual bit weight for scheduling algorithm
>> +      */
>> +     cx->weight = hweight64(cx->idxmsk64);
>
> So I think we talked about this a bit; what happens if CPU0 (taking your
> 4 core HSW-client) is first to program its counters and takes all 4 in
> exclusive mode?
>
> Then there's none left for CPU4.
>
> Did I miss where we avoid that problem, or is that an actual issue?

Yes, this patch series does not address this problem yet. It will be
in a second series.
Don't have a good solution yet.
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