[PATCH 12/33] perf, x86: Support full width counting

Andi Kleen
2012-10-26T20:36:54Z

Recent Intel CPUs have a new alternative MSR range for perfctrs that allows
writing the full counter width. Enable this range if the hardware reports it
using a new capability bit. This lowers overhead of perf stat slightly because
it has to do less interrupts to accumulate the counter value. On Haswell it
also avoids some problems with TSX aborting when the end of the counter
range is reached.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
arch/x86/include/asm/msr-index.h | 3 +++
arch/x86/kernel/cpu/perf_event.h | 1 +
arch/x86/kernel/cpu/perf_event_intel.c | 6 ++++++
3 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 7f0edce..2070f46 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -126,6 +126,9 @@
#define MSR_KNC_EVNTSEL0 0x00000028
#define MSR_KNC_EVNTSEL1 0x00000029

+/* Alternative perfctr range with full access. */
+#define MSR_IA32_PMC0 0x000004c1
+
/* AMD64 MSRs. Not complete. See the architecture manual for a more
complete list. */

diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
index e5da138..17cb08f 100644
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -278,6 +278,7 @@ union perf_capabilities {
u64 pebs_arch_reg:1;
u64 pebs_format:4;
u64 smm_freeze:1;
+ u64 fw_write:1;
};
u64 capabilities;
};
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 9502c19..9bff694 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -2238,5 +2238,11 @@ __init int intel_pmu_init(void)
}
}

+ /* Support full width counters using alternative MSR range */
+ if (x86_pmu.intel_cap.fw_write) {
+ x86_pmu.max_period = x86_pmu.cntval_mask;
+ x86_pmu.perfctr = MSR_IA32_PMC0;
+ }
+
return 0;
}
--
1.7.7.6