From 2e556b5b320838fde98480a1f6cf220a5af200fc Mon Sep 17 00:00:00 2001 From: Don Zickus Date: Thu, 2 Sep 2010 15:07:47 -0400 Subject: [PATCH] perf, x86: Fix accidentally ack'ing a second event on intel perf counter During testing of a patch to stop having the perf subsytem swallow nmis, it was uncovered that Nehalem boxes were randomly getting unknown nmis when using the perf tool. Moving the ack'ing of the PMI closer to when we get the status allows the hardware to properly re-set the PMU bit signaling another PMI was triggered during the processing of the first PMI. This allows the new logic for dealing with the shortcomings of multiple PMIs to handle the extra NMI by 'eat'ing it later. Now one can wonder why are we getting a second PMI when we disable all the PMUs in the begining of the NMI handler to prevent such a case, for that I do not know. But I know the fix below helps deal with this quirk. Tested on multiple Nehalems where the problem was occuring. With the patch, the code now loops a second time to handle the second PMI (whereas before it was not). Signed-off-by: Don Zickus Cc: peterz@infradead.org Cc: robert.richter@amd.com Cc: gorcunov@gmail.com Cc: fweisbec@gmail.com Cc: ying.huang@intel.com Cc: ming.m.lin@intel.com Cc: eranian@google.com LKML-Reference: <1283454469-1909-2-git-send-email-dzickus@redhat.com> Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/perf_event_intel.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c index d8d86d0..1297bf1 100644 --- a/arch/x86/kernel/cpu/perf_event_intel.c +++ b/arch/x86/kernel/cpu/perf_event_intel.c @@ -712,7 +712,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs) struct perf_sample_data data; struct cpu_hw_events *cpuc; int bit, loops; - u64 ack, status; + u64 status; perf_sample_data_init(&data, 0); @@ -728,6 +728,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs) loops = 0; again: + intel_pmu_ack_status(status); if (++loops > 100) { WARN_ONCE(1, "perfevents: irq loop stuck!\n"); perf_event_print_debug(); @@ -736,7 +737,6 @@ again: } inc_irq_stat(apic_perf_irqs); - ack = status; intel_pmu_lbr_read(); @@ -761,8 +761,6 @@ again: x86_pmu_stop(event); } - intel_pmu_ack_status(ack); - /* * Repeat if there is more work to be done: */ -- 2.7.4