x86, mmiotrace: fix buffer overrun detection

Impact: fix mmiotrace overrun tracing

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>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 9 deletions

diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
index f28484618ff0..e62cbf78eab6 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;
 }