linux-kernel - [PATCH 1/2] mmiotrace: fix buffer overrun detection

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Date:	Sun, 23 Nov 2008 21:24:30 +0200
From:	Pekka Paalanen <pq@....fi>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel <linux-kernel@...r.kernel.org>, fweisbec@...il.com
Subject: [PATCH 1/2] mmiotrace: fix buffer overrun detection

>From d5d72f3515ba3abffa317b985d7597718a024841 Mon Sep 17 00:00:00 2001
From: Pekka Paalanen <pq@....fi>
Date: Sun, 23 Nov 2008 19:18:18 +0200
Subject: [PATCH] mmiotrace: fix buffer overrun detection

When ftrace framework moved to use the ring buffer facility, the buffer
overrun detection was broken after 2.6.27 by commit

commit 3928a8a2d98081d1bc3c0a84a2d70e29b90ecf1c
Author: Steven Rostedt <rostedt@...dmis.org>
Date:   Mon Sep 29 23:02:41 2008 -0400

    ftrace: make work with new ring buffer

    This patch ports ftrace over to the new ring buffer.

The detection is now fixed by using the ring buffer API.

When mmiotrace detects a buffer overrun, it will report the number of
lost events. People reading an mmiotrace log must know if something was
missed, otherwise the data may not make sense.

Signed-off-by: Pekka Paalanen <pq@....fi>
---

Ingo, could these two patches still make it into .28?

 kernel/trace/trace_mmiotrace.c |   16 +++++++---------
 1 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
index f284846..e62cbf7 100644
--- a/kernel/trace/trace_mmiotrace.c
+++ b/kernel/trace/trace_mmiotrace.c
@@ -18,12 +18,14 @@ struct header_iter {
 
 static struct trace_array *mmio_trace_array;
 static bool overrun_detected;
+static unsigned long prev_overruns;
 
 static void mmio_reset_data(struct trace_array *tr)
 {
 	int cpu;
 
 	overrun_detected = false;
+	prev_overruns = 0;
 	tr->time_start = ftrace_now(tr->cpu);
 
 	for_each_online_cpu(cpu)
@@ -128,16 +130,12 @@ static void mmio_close(struct trace_iterator *iter)
 
 static unsigned long count_overruns(struct trace_iterator *iter)
 {
-	int cpu;
 	unsigned long cnt = 0;
-/* FIXME: */
-#if 0
-	for_each_online_cpu(cpu) {
-		cnt += iter->overrun[cpu];
-		iter->overrun[cpu] = 0;
-	}
-#endif
-	(void)cpu;
+	unsigned long over = ring_buffer_overruns(iter->tr->buffer);
+
+	if (over > prev_overruns)
+		cnt = over - prev_overruns;
+	prev_overruns = over;
 	return cnt;
 }
 
-- 
1.5.6.4

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