perf, x86: Prefer fixed-purpose counters when scheduling

This avoids a scheduling failure for cases like:

  cycles, cycles, instructions, instructions (on Core2)

Which would end up being programmed like:

  PMC0, PMC1, FP-instructions, fail

Because all events will have the same weight.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-8tnwb92asqj7xajqqoty4gel@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 14 insertions, 5 deletions

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index fa6fdec5afb..66f8ba9a67f 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -574,16 +574,25 @@ static bool __perf_sched_find_counter(struct perf_sched *sched)
 
         c = sched->constraints[sched->state.event];
 
+        /* Prefer fixed purpose counters */
+        if (x86_pmu.num_counters_fixed) {
+                idx = X86_PMC_IDX_FIXED;
+                for_each_set_bit_cont(idx, c->idxmsk, X86_PMC_IDX_MAX) {
+                        if (!__test_and_set_bit(idx, sched->state.used))
+                                goto done;
+                }
+        }
         /* Grab the first unused counter starting with idx */
         idx = sched->state.counter;
-        for_each_set_bit_cont(idx, c->idxmsk, X86_PMC_IDX_MAX) {
+        for_each_set_bit_cont(idx, c->idxmsk, X86_PMC_IDX_FIXED) {
                 if (!__test_and_set_bit(idx, sched->state.used))
-                        break;
+                        goto done;
         }
-        sched->state.counter = idx;
 
-        if (idx >= X86_PMC_IDX_MAX)
-                return false;
+        return false;
+
+done:
+        sched->state.counter = idx;
 
         if (c->overlap)
                 perf_sched_save_state(sched);