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

[Andi Kleen]

> I suppose that's fair that it's better for some use cases. The flip
> side is that it's no longer possible to get exactly accurate counts
> from user space if you're using the PMI (because any events between
> the overflow itself and the transition to the PMI handler are
> permanently lost) which is catastrophically bad for us :)

Yes that's a fair point. For most usages it doesn't matter.

I suspect that's a case for supporting opt-out for freezing
per perf event, and rr using that.

-Andi