Re: [PATCH v2 02/11] perf/x86: Improve HT workaround GP counter constraint

[Peter Zijlstra]

On Tue, May 26, 2015 at 04:33:42PM -0700, Andi Kleen wrote:
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
> > +		 */
> > +		if (is_ht_workaround_enabled() && !cpuc->is_fake &&
> 
> Could this function also check if at least one leaking event is
> scheduled somewhere? (e.g. from a global count)

You truncated one line too many:

+               if (is_ht_workaround_enabled() && !cpuc->is_fake &&
+                   READ_ONCE(cpuc->excl_cntrs->exclusive_present))
+                       gpmax /= 2;

Guess what that READ_ONCE() does? It checks if there's one such leaky
event on the current core.
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