Re: perf: WARNING perfevents: irq loop stuck!

[Ingo Molnar <mingo@kernel.org>]

* Vince Weaver <vincent.weaver@maine.edu> wrote:

> So this is just a warning, and I've reported it before, but the 
> perf_fuzzer triggers this fairly regularly on my Haswell system.
> 
> It looks like fixed counter 0 (retired instructions) being set to 
> 0000fffffffffffe occasionally causes an irq loop storm and gets 
> stuck until the PMU state is cleared.

So 0000fffffffffffe corresponds to 2 events left until overflow, 
right? And on Haswell we don't set x86_pmu.limit_period AFAICS, so we 
allow these super short periods.

Maybe like on Broadwell we need a quirk on Nehalem/Haswell as well, 
one similar to bdw_limit_period()? Something like the patch below?

Totally untested and such. I picked 128 because of Broadwell, but 
lower values might work as well. You could try to increase it to 3 and 
upwards and see which one stops triggering stuck NMI loops?

Thanks,

	Ingo

Signed-off-by: Ingo Molnar <mingo@kernel.org>

---
 arch/x86/kernel/cpu/perf_event_intel.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 960e85de13fb..26b13ea8299c 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -2479,6 +2479,15 @@ hsw_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
 
 	return c;
 }
+/*
+ * Really short periods might create infinite PMC NMI loops on Haswell,
+ * so limit them to 128. There's no official erratum for this AFAIK.
+ */
+static unsigned int hsw_limit_period(struct perf_event *event, unsigned int left)
+{
+	return max(left, 128U);
+}
+
 
 /*
  * Broadwell:
@@ -2495,7 +2504,7 @@ hsw_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
  * Therefore the effective (average) period matches the requested period,
  * despite coarser hardware granularity.
  */
-static unsigned bdw_limit_period(struct perf_event *event, unsigned left)
+static unsigned int bdw_limit_period(struct perf_event *event, unsigned left)
 {
 	if ((event->hw.config & INTEL_ARCH_EVENT_MASK) ==
 			X86_CONFIG(.event=0xc0, .umask=0x01)) {
@@ -3265,6 +3274,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.hw_config = hsw_hw_config;
 		x86_pmu.get_event_constraints = hsw_get_event_constraints;
 		x86_pmu.cpu_events = hsw_events_attrs;
+		x86_pmu.limit_period = hsw_limit_period;
 		x86_pmu.lbr_double_abort = true;
 		pr_cont("Haswell events, ");
 		break;