Re: [PATCH] perf, x86: Add workaround for MEM_*_RETIRED errata BV98

[Stephane Eranian]

On Wed, May 1, 2013 at 9:13 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
>> Unfortunately, Andi's patch fails to correct the problem though
>> it is the right approach. As he said, the problem is unfortunately
>
> perf stat -a / record -a / top will work.
>
But it does not for perf stat -a. Look at my example, run it on your machine.

> The case it doesn't fix is per thread when the other sibling
> is not running a counter.
>
> Essentially with the patch you may still get under-counting
> on these specific events if they run per thread (or are really
> unlucky in multiplexing), but never over-counting on anything.
>
> In the past Ingo's guidance was to focus on the most common
> use cases, which I think this patch does.
>
> It would be possible to fix the per thread mode too, but it would
> need quite a bit of new infrastructure and I have doubts that's
> worth it.
>
> -Andi
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