linux-kernel - [PATCH] perf, x86: Make cycles:p working on SNB

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Date:	Thu, 24 May 2012 12:02:05 +0900
From:	Namhyung Kim <namhyung.kim@....com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>
Cc:	Namhyung Kim <namhyung@...il.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Paul Mackerras <paulus@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] perf, x86: Make cycles:p working on SNB

The Intel SDM (Vol.3B 18-55, Table 18-21) says the PEBS
is only work for INST_RETIRED.PREC_DIST (0x01C0) and it's
applied into intel_snb_pebs_event_constraints already.
Thus, current alt_config which has umake set to 0 cannot
work on SNBs and the output will look like below:

 namhyung@...ong:perf$ ./perf stat -e cycles:p noploop 1

 Performance counter stats for 'noploop 1':

   <not supported> cycles

       1.001116732 seconds time elapsed

After applying this patch, the event is counted properly.

Signed-off-by: Namhyung Kim <namhyung.kim@....com>
---
 arch/x86/kernel/cpu/perf_event_intel.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 166546ec6aef..db8948171e22 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1329,6 +1329,12 @@ static int intel_pmu_hw_config(struct perf_event *event)
 		 */
 		u64 alt_config = X86_CONFIG(.event=0xc0, .inv=1, .cmask=16);
 
+		/*
+		 * SNB introduced INST_RETIRED.PREC_DIST for this purpose.
+		 */
+		if (x86_pmu.pebs_constraints == intel_snb_pebs_event_constraints)
+			alt_config = X86_CONFIG(.event=0xc0, .umask=0x01,
+						.inv=1, .cmask=16);
 
 		alt_config |= (event->hw.config & ~X86_RAW_EVENT_MASK);
 		event->hw.config = alt_config;
-- 
1.7.10.1

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