Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter

From	Andi Kleen <ak@linux.intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter
Date	2017-05-30 19:30 +0200
Message-ID	<tMT7Y-1Nk-7@gated-at.bofh.it> (permalink)
References	(5 earlier) <tKH1f-4vB-5@gated-at.bofh.it> <tMd8J-6Ob-13@gated-at.bofh.it> <tMLDs-5ux-37@gated-at.bofh.it> <tMPQK-861-9@gated-at.bofh.it> <tMSbU-1dJ-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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> > You would only need a single one per system however, not one per CPU.
> > RCU already tracks all the CPUs, all we need is a single NMI watchdog
> > that makes sure RCU itself does not get stuck.
> > 
> > So we just have to find a single watchdog somewhere that can trigger
> > NMI.
> 
> But then you have to IPI broadcast the NMI, which is less than ideal.

Only when the watchdog times out to print the backtraces.

> 
> RCU doesn't have that problem because the quiescent state is a global
> thing. CPU progress, which is what the NMI watchdog tests, is very much
> per logical CPU though.

RCU already has a CPU stall detector. It should work (and usually
triggers before the NMI watchdog in my experience unless the
whole system is dead)

-Andi

Thread

Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Stephane Eranian <eranian@google.com> - 2017-05-28 22:40 +0200
  Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Peter Zijlstra <peterz@infradead.org> - 2017-05-30 11:30 +0200
    Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Andi Kleen <ak@linux.intel.com> - 2017-05-30 16:00 +0200
      Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Peter Zijlstra <peterz@infradead.org> - 2017-05-30 18:30 +0200
        Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Stephane Eranian <eranian@google.com> - 2017-05-30 18:50 +0200
        Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Andi Kleen <ak@linux.intel.com> - 2017-05-30 19:30 +0200
          Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Peter Zijlstra <peterz@infradead.org> - 2017-05-30 19:50 +0200
            Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Andi Kleen <ak@linux.intel.com> - 2017-05-30 20:00 +0200
              Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Peter Zijlstra <peterz@infradead.org> - 2017-05-30 21:10 +0200
                Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Andi Kleen <ak@linux.intel.com> - 2017-05-30 21:50 +0200
    Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Stephane Eranian <eranian@google.com> - 2017-05-30 18:50 +0200
      Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP  counter Thomas Gleixner <tglx@linutronix.de> - 2017-05-30 19:00 +0200

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