Messages in this thread | | | Date | Tue, 30 May 2017 10:22:08 -0700 | From | Andi Kleen <> | Subject | Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter |
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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
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