Messages in this thread | | | Date | Thu, 18 Nov 2021 13:20:09 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 03/13] perf/x86/amd: add AMD Fam19h Branch Sampling support |
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On Tue, Nov 16, 2021 at 11:23:39PM -0800, Stephane Eranian wrote: > On Tue, Nov 16, 2021 at 12:29 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > > On Mon, Nov 15, 2021 at 11:48:01PM -0800, Stephane Eranian wrote: > > > On Fri, Nov 12, 2021 at 8:02 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > > > On Thu, Nov 11, 2021 at 12:44:05AM -0800, Stephane Eranian wrote: > > > > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c > > > > > index 38b2c779146f..28559557f966 100644 > > > > > --- a/arch/x86/events/core.c > > > > > +++ b/arch/x86/events/core.c > > > > > @@ -683,11 +683,16 @@ void x86_pmu_disable_all(void) > > > > > > > > > > if (!test_bit(idx, cpuc->active_mask)) > > > > > continue; > > > > > + > > > > > + if (is_amd_brs(hwc)) > > > > > + amd_brs_disable(); > > > > > + > > > > > rdmsrl(x86_pmu_config_addr(idx), val); > > > > > if (!(val & ARCH_PERFMON_EVENTSEL_ENABLE)) > > > > > continue; > > > > > val &= ~ARCH_PERFMON_EVENTSEL_ENABLE; > > > > > wrmsrl(x86_pmu_config_addr(idx), val); > > > > > + > > > > > if (is_counter_pair(hwc)) > > > > > wrmsrl(x86_pmu_config_addr(idx + 1), 0); > > > > > } > > > > > > > > Please, stick that in amd_pmu_disable_all(). > > > > > > > > > If I do that, I need to add a for_each_counter() loop to > > > amd_pmu_disable_all() but it does not have one call systematically. > > > If you are okay with it, then I am fine as well. > > > > Why ? There is only one BRS you can disable it first, and then do the > > loop. Same on the enable_all side, enable it once, not per event. > > ->add/->del can keep a per-event count for sharing purposes, but you > > don't need that for {en,dis}able_all, right? > > Ok, I made the changes you suggested. It looks closer to the way LBR is handled. > However, this means that there is no path by which you can get to > amd_pmu_disable_event() > without having gone through amd_pmu_disable_all(). Is that always the > case? And same thing > on the enable side.
So that's true for ->add() and ->del(), those cannot be called without being wrapped in ->pmu_disable(), ->pmu_enable().
There is however the ->stop() and ->start() usage for throttling, which can stop an individual event (while leaving the event scheduled on the PMU). Now, I think the ->stop() gets called with the PMU enabled, but the ->start() is with it disabled again.
The ramification would be that we'd stop the event, but leave BRS enabled for a throttled event. Which should be harmless, no?
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