Messages in this thread | | | Date | Thu, 14 Mar 2013 18:06:41 -0700 | Subject | Re: [GIT PULL] perf fixes | From | Linus Torvalds <> |
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On Thu, Mar 14, 2013 at 5:24 PM, Stephane Eranian <eranian@google.com> wrote: > > I bet if you force the affinity of your perf record to be on > a CPU other than CPU0, you will not get the crash. > > This is what I am seeing now. I appears on resume, > CPU0 hotplug callbacks for perf_events are not invoked > leaving DS_AREA MSR to 0. > > Can you confirm on your machine?
I'm not even going to bother confirming it, because I think you're right, and I think the reason is clear: the DS initialization code uses the CPU_UP notifiers.
And that's sufficient for CPU hotplug, which is what suspend/resume ends up doing for all but the boot CPU. But the boot CPU is not hotplugged.
Using CPU_UP notifiers is wrong, and they get called too late anyway.
The code should use a real resume method. Or, better yet, just do it right, and do it from __restore_processor_state().
Those f*cking CPU notifiers are a pain in the ass, and the tend to be invariably broken, and they have their own idiotic hacks that are equally broken (ie that x86_pmu_notifier() thing seems to make up its own suspend/resume with "x86_pmu.cpu_prepare/cpu_starting/cpu_dying/cpu_dead" things.
I guess we could make the BP do a fake cpu notifier thing around the suspend of the boot processor as well, but most of the per-CPU stuff seems to be perfectly fine without it (ie mtrr, apic, etc etc all use the suspend/resume infrastructure) and doesn't need that kind of stuff.
Linus
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