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Subject[PATCH 1/2] mmiotrace: fix buffer overrun detection
From d5d72f3515ba3abffa317b985d7597718a024841 Mon Sep 17 00:00:00 2001
From: Pekka Paalanen <pq@iki.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@goodmis.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@iki.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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