Re: [PATCH -v3] perf, x86: try to handle unknown nmis with running perfctrs

Don Zickus
2010-08-20T01:50:42Z

On Thu, Aug 19, 2010 at 04:27:13PM +0200, Peter Zijlstra wrote:
> On Thu, 2010-08-19 at 10:12 -0400, Don Zickus wrote:
> > On Thu, Aug 19, 2010 at 12:45:53PM +0200, Peter Zijlstra wrote:
> > >
> > > I queued it with that part changed to:
> >
> > I realized the other day this change doesn't cover the nehalem, core and p4
> > cases which use
> >
> > intel_pmu_handle_irq
> > p4_pmu_handle_irq
> >
> > as their handlers. Though that patch can go on top of Robert's.
>
> Something like this?

I tested this patch and Robert's on an AMD box and Nehalem box. Both
worked as intended. However I did notice that whenever the AMD box
detected handled >1, it was shortly followed by an unknown_nmi that was
properly eaten with Robert's logic. Whereas on the Nehalem box I saw a
lot of 'handled > 1' messages but very very few of them were followed by
an unknown_nmi message (and those messages that did come were properly
eaten).

Maybe that is just the differences in the cpu designs.

Of course I had to make the one change I mentioned previously for the
perf_event_intel.c file (moving the handled++ logic down a few lines).

I didn't run the test on a P4 box.

Looks great, thanks guys!

Cheers,
Don

>
> ---
> Index: linux-2.6/arch/x86/kernel/cpu/perf_event_intel.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/cpu/perf_event_intel.c
> +++ linux-2.6/arch/x86/kernel/cpu/perf_event_intel.c
> @@ -713,6 +713,7 @@ static int intel_pmu_handle_irq(struct p
> struct cpu_hw_events *cpuc;
> int bit, loops;
> u64 ack, status;
> + int handled = 0;
>
> perf_sample_data_init(&data, 0);
>
> @@ -743,12 +744,16 @@ again:
> /*
> * PEBS overflow sets bit 62 in the global status register
> */
> - if (__test_and_clear_bit(62, (unsigned long *)&status))
> + if (__test_and_clear_bit(62, (unsigned long *)&status)) {
> + handled++;
> x86_pmu.drain_pebs(regs);
> + }
>
> for_each_set_bit(bit, (unsigned long *)&status, X86_PMC_IDX_MAX) {
> struct perf_event *event = cpuc->events[bit];
>
> + handled++;
> +
> if (!test_bit(bit, cpuc->active_mask))
> continue;
>
> @@ -772,7 +777,7 @@ again:
>
> done:
> intel_pmu_enable_all(0);
> - return 1;
> + return handled;
> }
>
> static struct event_constraint *
> Index: linux-2.6/arch/x86/kernel/cpu/perf_event_p4.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/cpu/perf_event_p4.c
> +++ linux-2.6/arch/x86/kernel/cpu/perf_event_p4.c
> @@ -673,7 +673,7 @@ static int p4_pmu_handle_irq(struct pt_r
> if (!overflow && (val & (1ULL << (x86_pmu.cntval_bits - 1))))
> continue;
>
> - handled += overflow;
> + handled += !!overflow;
>
> /* event overflow for sure */
> data.period = event->hw.last_period;
> @@ -690,7 +690,7 @@ static int p4_pmu_handle_irq(struct pt_r
> inc_irq_stat(apic_perf_irqs);
> }
>
> - return handled > 0;
> + return handled;
> }
>
> /*
>