ring-buffer: Add a 'dropped events' counter

The existing 'overrun' counter is incremented when the ring
buffer wraps around, with overflow on (the default). We wanted
a way to count requests lost from the buffer filling up with
overflow off, too. I decided to add a new counter instead
of retro-fitting the existing one because it seems like a
different statistic to count conceptually, and also because
of how the code was structured.

Link: http://lkml.kernel.org/r/1310765038-26399-1-git-send-email-slavapestov@google.com

Signed-off-by: Slava Pestov <slavapestov@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f6928edacd6d..36c213fbfce7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4385,6 +4385,9 @@ tracing_stats_read(struct file *filp, char __user *ubuf,
         usec_rem = do_div(t, USEC_PER_SEC);
         trace_seq_printf(s, "now ts: %5llu.%06lu\n", t, usec_rem);
 
+        cnt = ring_buffer_dropped_events_cpu(tr->buffer, cpu);
+        trace_seq_printf(s, "dropped events: %ld\n", cnt);
+
         count = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->len);
 
         kfree(s);