linux-kernel - [PATCH 02/11] perf: Do not get values from disabled counters in group format read

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Date:	Sat, 20 Oct 2012 16:33:10 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: [PATCH 02/11] perf: Do not get values from disabled counters in group format read

It's possible some of the counters in the group could be
disabled when sampling member of the event group is reading
the rest via PERF_SAMPLE_READ sample type processing. Disabled
counters could then produce wrong numbers.

Fixing that by reading only enabled counters for PERF_SAMPLE_READ
sample type processing.

Signed-off-by: Jiri Olsa <jolsa@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Namhyung Kim <namhyung@...nel.org>
---
 kernel/events/core.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 32aec40..5220d01 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4012,12 +4012,24 @@ static void perf_output_read_group(struct perf_output_handle *handle,
 	__output_copy(handle, values, n * sizeof(u64));
 
 	list_for_each_entry(sub, &leader->sibling_list, group_entry) {
+		u64 value = 0;
 		n = 0;
 
-		if (sub != event)
-			sub->pmu->read(sub);
+		/*
+		 * We are NOT interested in disabled counters,
+		 * giving us strange values and keeping us from
+		 * good night sleep!!!
+		 */
+		if (sub->state > PERF_EVENT_STATE_OFF) {
+
+			if (sub != event)
+				sub->pmu->read(sub);
+
+			value = perf_event_count(sub);
+		}
+
+		values[n++] = value;
 
-		values[n++] = perf_event_count(sub);
 		if (read_format & PERF_FORMAT_ID)
 			values[n++] = primary_event_id(sub);
 
-- 
1.7.11.4

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