Re: [REGRESSION] x86, perf: counter freezing breaks rr

[Peter Zijlstra]

On Tue, Nov 20, 2018 at 02:38:54PM -0800, Andi Kleen wrote:
> > In fact, I'll argue FREEZE_ON_OVERFLOW is unfixably broken for
> > independent counters, because while one counter overflows, we'll stall
> > counting on all others until we've handled the PMI.
> > 
> > Even though the PMI might not be for them and they very much want/need
> > to continue counting.
> 
> We stop all counters in any case for the PMI. With freeze-on-PMI it just
> happens slightly earlier.

Hiding the PMI is fine and good. The PMI is not the workload. Stopping
it earlier is _NOT_ good, it hides your actual workload.