Re: [PATCH] perf/x86/amd/ibs: Fix sample bias for dispatched micro-ops

On Mon, Aug 26, 2019 at 02:57:30PM -0500, Kim Phillips wrote: > diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c > index 62f317c9113a..f2625b4a5a8b 100644 > --- a/arch/x86/events/amd/ibs.c > +++ b/arch/x86/events/amd/ibs.c > @@ -663,8 +663,15 @@ static int perf_ibs_handle_irq(str

[PATCH] perf/x86/amd/ibs: Fix sample bias for dispatched micro-ops

When counting dispatched micro-ops with cnt_ctl=1, in order to prevent sample bias, IBS hardware preloads the least significant 7 bits of current count (IbsOpCurCnt) with random values, such that, after the interrupt is handled and counting resumes, the next sample taken will be slightly perturbed.