Re: [PATCH v2 0/12] perf/x86: implement HT leak workaround for SNB/IVB/HSW

[Peter Zijlstra]

On Tue, Oct 21, 2014 at 02:28:06PM +0200, Stephane Eranian wrote:
> Peter,
> 
> On Tue, Oct 21, 2014 at 1:25 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> >
> > lkml.kernel.org/r/CABPqkBRbst4sgpgE5O_VXt-CSC0VD=aP2KWA0e3Uy64tw7df3A@xxxxxxxxxxxxxx
> >
> > I missed that 3 lines if they were in here.
> >
> I did not put them in there because there is another problem.
> If you partition the generic counters 2 and 2, then some CPUs will not
> be able to measure some events.
> Unfortunately, there is no way to partition the 4 counters such that
> all the events can be measured by
> each CPU. Some events or precise sampling requires counter 2 for
> instance (like prec_dist).
> That's why I did not put this fix in.

Ah, I wasn't thinking about a hard partition, just a limit on the number
of exclusive counters any one CPU can claim such as to not starve. Or is
that what you were talking about? I feel not being able to starve
another CPU is more important than a better utilization bound for
counter scheduling.
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