linux-kernel - [PATCH 16/31] perf, x86: Support full width counting on Haswell

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Date:	Thu, 27 Sep 2012 21:31:21 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	linux-kernel@...r.kernel.org
Cc:	x86@...nel.org, a.p.zijlstra@...llo.nl, eranian@...gle.com,
	acme@...hat.com, Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH 16/31] perf, x86: Support full width counting on Haswell

From: Andi Kleen <ak@...ux.intel.com>

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@...ux.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 957ec87..cbf344f 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -121,6 +121,9 @@
 #define MSR_P6_EVNTSEL0			0x00000186
 #define MSR_P6_EVNTSEL1			0x00000187
 
+/* 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 8200c69..8550601 100644
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -282,6 +282,7 @@ 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 cd48669..e302186 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -2188,5 +2188,11 @@ __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

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