perf/x86: Fix uncore PCI fixed counter handling

There was a bug in the handling of SNB-EP/IVB-EP uncore PCI
fixed counters, e.g., IMC.

It would cause erratic values to be returned for the IMC
clockticks event. This was due to a bogus hwc->config value
which was then written to PCI config space.

The erratic values can be seen via:

  $ perf stat -a -C 0 -e uncore_imc_0/clockticks/ -I 1000 sleep 10

The fixed counter has most fields marked as reserved with
hw reset values of 0. Yet the kernel was defaulting to a
hwc->config = ~0 and that was causing the issues.

This patch sets the hwc->config values for fixed uncore event
to 0. Now, the values of IMC clockticks is correct.

Signed-off-by: Stephane Eranian <eranian@google.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: peterz@infradead.org
Cc: zheng.z.yan@intel.com
Link: http://lkml.kernel.org/r/20130909195350.GA17643@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore.c b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
index fd8011e..8ed4458 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event_intel_uncore.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
@@ -2808,7 +2808,7 @@ uncore_get_event_constraint(struct intel_uncore_box *box, struct perf_event *eve
                        return c;
        }
 
-       if (event->hw.config == ~0ULL)
+       if (event->attr.config == UNCORE_FIXED_EVENT)
                return &constraint_fixed;
 
        if (type->constraints) {
@@ -3112,7 +3112,9 @@ static int uncore_pmu_event_init(struct perf_event *event)
                 */
                if (pmu->type->single_fixed && pmu->pmu_idx > 0)
                        return -EINVAL;
-               hwc->config = ~0ULL;
+
+               /* fixed counters have event field hardcoded to zero */
+               hwc->config = 0ULL;
        } else {
                hwc->config = event->attr.config & pmu->type->event_mask;
                if (pmu->type->ops->hw_config) {