[PATCH 13/34] perf, x86: Support full width counting on Haswell

Andi Kleen
2012-10-18T23:28:12Z

Haswell has 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. 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 7ddbc3d..740d6b2 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -2230,5 +2230,11 @@ __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