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 21:50 +0200
Message-ID	<tMVjs-34l-25@gated-at.bofh.it> (permalink)
References	(5 earlier) <tMSbU-1dJ-15@gated-at.bofh.it> <tMT7Y-1Nk-7@gated-at.bofh.it> <tMTrj-1TY-7@gated-at.bofh.it> <tMTB1-1Xw-29@gated-at.bofh.it> <tMUGJ-2PS-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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> > BTW there's an alternative solution in cycling the NMI watchdog over
> > all available CPUs. Then it would eventually cover all. But that's
> > less real time friendly than relying on RCU.
> 
> I don't think we need to worry too much about the watchdog being rt
> friendly. Robustness is the thing that worries me most.

Ok. Then just cycling is the most robust method, and it's very
simple.

You're right. Perhaps it's better than to rely on the RCU machinery which
seems to become ever more and more complex.

People who care extremely about latencies can just turn it off.

The main problem with the proposal is that it depends on the BIOS not 
locking the TCO watchdog. On the systems were it is locked we would
either need to continue using the PMU for the watchdog, or find some other 
watchdog source that can be programmed to be a NMI.

-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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