Messages in this thread | | | Date | Tue, 2 Apr 2019 15:03:02 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH v3 0/3] x86/perf/amd: AMD PMC counters and NMI latency |
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On Mon, Apr 01, 2019 at 09:46:33PM +0000, Lendacky, Thomas wrote: > This patch series addresses issues with increased NMI latency in newer > AMD processors that can result in unknown NMI messages when PMC counters > are active. > > The following fixes are included in this series: > > - Resolve a race condition when disabling an overflowed PMC counter, > specifically when updating the PMC counter with a new value. > - Resolve handling of active PMC counter overflows in the perf NMI > handler and when to report that the NMI is not related to a PMC. > - Remove earlier workaround for spurious NMIs by re-ordering the > PMC stop sequence to disable the PMC first and then remove the PMC > bit from the active_mask bitmap. As part of disabling the PMC, the > code will wait for an overflow to be reset. > > The last patch re-works the order of when the PMC is removed from the > active_mask. There was a comment from a long time ago about having > to clear the bit in active_mask before disabling the counter because > the perf NMI handler could re-enable the PMC again. Looking at the > handler today, I don't see that as possible, hence the reordering. The > question will be whether the Intel PMC support will now have issues. > There is still support for using x86_pmu_handle_irq() in the Intel > core.c file. Did Intel have any issues with spurious NMIs in the past? > Peter Z, any thoughts on this?
I can't remember :/ I suppose we'll see if anything pops up after these here patches. At least then we get a chance to properly document things.
> Also, I couldn't completely get rid of the "running" bit because it > is used by arch/x86/events/intel/p4.c. An old commit comment that > seems to indicate the p4 code suffered the spurious interrupts: > 03e22198d237 ("perf, x86: Handle in flight NMIs on P4 platform"). > So maybe that partially answers my previous question...
Yeah, the P4 code is magic, and I don't have any such machines left, nor do I think does Cyrill who wrote much of that.
I have vague memories of the P4 thing crashing with Vince's perf_fuzzer, but maybe I'm wrong.
Ideally we'd find a willing victim to maintain that thing, or possibly just delete it, dunno if anybody still cares.
Anyway, I like these patches, but I cannot apply since you send them base64 encoded and my script chokes on that.
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