perf: honouring the cpuid for number of fixed counters in hypervisors

RFC PATCH Superseded Imre Palik 2 participants 2 messages Oct 13, 2016 – Oct 16, 2016

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Imre Palik

author

2016-10-13 08:41 UTC #0 lore raw

RFC PATCH 1/1 perf: honouring the cpuid for number of fixed counters in hypervisors

From: Imre Palik <[email protected]>

perf doesn't seem to honour the number of fixed counters specified by cpuid leaf 0xa. It always assume that Intel CPUs have at least 3 fixed counters.

So if some of the fixed counters are masked out by the hypervisor, it still tries to check/set them.

This patch makes perf behave nicer when the kernel is running under a hypervisor that doesn't expose all the counters.

This patch contains some ideas from Matt Wilson.

Signed-off-by Imre Palik <[email protected]>

Cc Matt Wilson <[email protected]>

---
 arch/x86/events/intel/core.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

arch/x86/events/intel/core.c +11 -3

index a3a9eb8..12ca3f9 100644
@@ -3607,10 +3607,18 @@ __init int intel_pmu_init(void)
 
 	/*
 	 * Quirk: v2 perfmon does not report fixed-purpose events, so
-	 * assume at least 3 events:
+	 * assume at least 3 events, when not running in a hypervisor:
 	 */
-	if (version > 1)
-		x86_pmu.num_counters_fixed = max((int)edx.split.num_counters_fixed, 3);
+	if (version > 1) {
+		unsigned int ecx = cpuid_ecx(1);
+
+		if (ecx >> 31)
+			x86_pmu.num_counters_fixed =
+				edx.split.num_counters_fixed;
+		else
+			x86_pmu.num_counters_fixed =
+				max((int)edx.split.num_counters_fixed, 3);
+	}
 
 	if (boot_cpu_has(X86_FEATURE_PDCM)) {
 		u64 capabilities;

Signature · 1 line

2.10.1

Peter Zijlstra

maintainer

2016-10-16 13:51 UTC #1 lore raw

arch/x86/events/intel/core.c __init int intel_pmu_init(void) · line 3615

Quoted 4 lines · Imre Palik

arch/x86/events/intel/core.c +4 -0

+	if (version > 1) {
+		unsigned int ecx = cpuid_ecx(1);
+
+		if (ecx >> 31)

What is this magic, undocumented gunk doing? Is that supposed to be static_cpu_has(X86_FEATURE_HYPERVISOR) ?