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>

1 files changed, 4 insertions, 2 deletions

diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore.c b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
index fd8011ed4dcd..8ed44589b0e4 100644
--- 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) {