2016-10-21 08:19:35

by Imre Palik

Subject: [RFC PATCH v2] 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]>
Cc: David Woodhouse <[email protected]>
---
arch/x86/events/intel/core.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index a3a9eb8..e06d071 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3607,10 +3607,14 @@ __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) {
+ if (static_cpu_has(X86_FEATURE_HYPERVISOR))
+ 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;
--
2.10.1

2016-10-24 16:50:05

by Andi Kleen

Subject: Re: [RFC PATCH v2] perf: honouring the cpuid for number of fixed counters in hypervisors

On Fri, Oct 21, 2016 at 01:18:59AM -0700, Imre Palik wrote:
> 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.

Patch looks good to me.

Reviewed-by: Andi Kleen <[email protected]>

-Andi

2016-10-26 09:20:18

by Peter Zijlstra

Subject: Re: [RFC PATCH v2] perf: honouring the cpuid for number of fixed counters in hypervisors

On Fri, Oct 21, 2016 at 01:18:59AM -0700, Imre Palik wrote:
> +++ b/arch/x86/events/intel/core.c
> @@ -3607,10 +3607,14 @@ __init int intel_pmu_init(void)
>
> /*
> * Quirk: v2 perfmon does not report fixed-purpose events, so
> + * assume at least 3 events, when not running in a hypervisor:
> */
> + if (version > 1) {
> + if (static_cpu_has(X86_FEATURE_HYPERVISOR))
> + x86_pmu.num_counters_fixed = edx.split.num_counters_fixed;
> + else
> + x86_pmu.num_counters_fixed = max((int)edx.split.num_counters_fixed, 3);
> + }


I made that:

/*
* Quirk: v2 perfmon does not report fixed-purpose events, so
+ * assume at least 3 events, when not running in a hypervisor:
*/
+ if (version > 1) {
+ int assume = 3 * !boot_cpu_has(X86_FEATURE_HYPERVISOR);
+
+ x86_pmu.num_counters_fixed =
+ max((int)edx.split.num_counters_fixed, assume);
+ }


Thanks!

2016-10-28 10:14:58

by tip-bot for Vasyl Gomonovych

Subject: [tip:perf/urgent] perf/x86/intel: Honour the CPUID for number of fixed counters in hypervisors

Commit-ID: f92b7604149a55cb601fc0b52911b1e11f0f2514
Gitweb: http://git.kernel.org/tip/f92b7604149a55cb601fc0b52911b1e11f0f2514
Author: Imre Palik <[email protected]>
AuthorDate: Fri, 21 Oct 2016 01:18:59 -0700
Committer: Ingo Molnar <[email protected]>
CommitDate: Fri, 28 Oct 2016 11:06:25 +0200

perf/x86/intel: Honour the CPUID for number of fixed counters in hypervisors

perf doesn't seem to honour the number of fixed counters specified by CPUID
leaf 0xa. It always assumes 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]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Andi Kleen <[email protected]>
Cc: Alexander Kozyrev <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Artyom Kuanbekov <[email protected]>
Cc: David Carrillo-Cisneros <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Matt Wilson <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/events/intel/core.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index eab0915..a74a2db 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3607,10 +3607,14 @@ __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) {
+ int assume = 3 * !boot_cpu_has(X86_FEATURE_HYPERVISOR);
+
+ x86_pmu.num_counters_fixed =
+ max((int)edx.split.num_counters_fixed, assume);
+ }

if (boot_cpu_has(X86_FEATURE_PDCM)) {
u64 capabilities;