[tip:perf/core] perf, x86: Prefer fixed-purpose counters when scheduling

[tip-bot for Peter Zijlstra]

Commit-ID:  4defea8559bc0f97a899d94c8d19d3b8bb802bc4
Gitweb:     http://git.kernel.org/tip/4defea8559bc0f97a899d94c8d19d3b8bb802bc4
Author:     Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Thu, 10 Nov 2011 15:15:42 +0100
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 6 Dec 2011 08:33:58 +0100

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@xxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-8tnwb92asqj7xajqqoty4gel@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 arch/x86/kernel/cpu/perf_event.c |   19 ++++++++++++++-----
 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 fa6fdec..66f8ba9 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);
--
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