From ae0def05ed856343181bf1eca4fab3e09056df6d Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Thu, 30 May 2013 10:45:59 -0700 Subject: [PATCH] perf/x86: Only print PMU state when also WARN()'ing intel_pmu_handle_irq() has a warning in it if it does too many loops. It is a WARN_ONCE(), but the perf_event_print_debug() call beneath it is unconditional. For the first warning, you get a nice backtrace and message, but subsequent ones just dump the PMU state with no leading messages. I doubt this is what was intended. This patch will only print the PMU state when paired with the WARN_ON() text. It effectively open-codes WARN_ONCE()'s one-time-only logic. My suspicion is that the code really just wants to make sure we do not sit in the loop and spit out a warning for every loop iteration after the 100th. From what I've seen, this is very unlikely to happen since we also clear the PMU state. After this patch, instead of seeing the PMU state dumped each time, you will just see: [57494.894540] perf_event_intel: clearing PMU state on CPU#129 [57579.539668] perf_event_intel: clearing PMU state on CPU#10 [57587.137762] perf_event_intel: clearing PMU state on CPU#134 [57623.039912] perf_event_intel: clearing PMU state on CPU#114 [57644.559943] perf_event_intel: clearing PMU state on CPU#118 ... Signed-off-by: Dave Hansen Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20130530174559.0DB049F4@viggo.jf.intel.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/perf_event_intel.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c index a9e22073bd56..1321cf8fa817 100644 --- a/arch/x86/kernel/cpu/perf_event_intel.c +++ b/arch/x86/kernel/cpu/perf_event_intel.c @@ -1188,8 +1188,12 @@ static int intel_pmu_handle_irq(struct pt_regs *regs) again: intel_pmu_ack_status(status); if (++loops > 100) { - WARN_ONCE(1, "perfevents: irq loop stuck!\n"); - perf_event_print_debug(); + static bool warned = false; + if (!warned) { + WARN(1, "perfevents: irq loop stuck!\n"); + perf_event_print_debug(); + warned = true; + } intel_pmu_reset(); goto done; } -- GitLab