Re: [BUG] Core2 cpu triggers hard lockup with perf test

Peter Zijlstra
2016-03-01T18:14:16Z

On Tue, Mar 01, 2016 at 07:04:40PM +0100, Jiri Olsa wrote:

> > That's the PERF_GLOBAL_CTRL, right? But it must have succeeded,
>
> yep, should be this one:
>
> static void __intel_pmu_enable_all(int added, bool pmi)
> {
> struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>
> intel_pmu_pebs_enable_all();
> intel_pmu_lbr_enable_all(pmi);
> >>> wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL,
> x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_guest_mask);
>
>
> > otherwise the NMI watchdog would never have fired.
>
> so NMI wouldn't trigger if CPU is inside wrmsr?

Well, anything goes with MSR writes, that's all a magic heap of
micro-code.

But at the very least it did actually enable the counters, otherwise the
counter used for the NMI watchdog could not fire, it too would still be
disabled.