linux-kernel - [PATCH 2/9] metag: perf: fix wrap handling in delta calculation

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Date:	Fri, 15 Mar 2013 13:43:41 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	<linux-kernel@...r.kernel.org>
CC:	James Hogan <james.hogan@...tec.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: [PATCH 2/9] metag: perf: fix wrap handling in delta calculation

When calculating the delta, mask with MAX_PERIOD (24 bits) to handle
wrapping, which particularly happens with periodic sampling since the
value is intentionally set so that it will overflow soon.

Signed-off-by: James Hogan <james.hogan@...tec.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
---
 arch/metag/kernel/perf/perf_event.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/metag/kernel/perf/perf_event.c b/arch/metag/kernel/perf/perf_event.c
index f38bf6d..8096db2 100644
--- a/arch/metag/kernel/perf/perf_event.c
+++ b/arch/metag/kernel/perf/perf_event.c
@@ -211,7 +211,7 @@ again:
 	/*
 	 * Calculate the delta and add it to the counter.
 	 */
-	delta = new_raw_count - prev_raw_count;
+	delta = (new_raw_count - prev_raw_count) & MAX_PERIOD;
 
 	local64_add(delta, &event->count);
 }
-- 
1.8.1.2


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