linux-kernel - [PATCH 2/2] kernel/events: Add option to enable counting sideband events in wakeup

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Date:   Mon, 19 Jun 2017 20:01:08 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] kernel/events: Add option to enable counting sideband events in wakeup_events

Many sideband events are interesting by themselves. When profiling only
for sideband events, it is useful to be able to control process wakeup
(wakeup_events) based on sideband events alone. Add a new option
'count_sb_events' to do the same.

Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
 include/uapi/linux/perf_event.h |  3 ++-
 kernel/events/core.c            |  4 ++--
 kernel/events/ring_buffer.c     | 13 +++++++++++++
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index e5810b1d74a4..ab4dc9a02151 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -346,7 +346,8 @@ struct perf_event_attr {
 				write_backward :  1, /* Write ring buffer from end to beginning */
 				namespaces     :  1, /* include namespaces data */
 				signal_on_wakeup : 1, /* send signal on wakeup */
-				__reserved_1   : 34;
+				count_sb_events  : 1, /* wakeup_events also counts sideband events */
+				__reserved_1   : 33;
 
 	union {
 		__u32		wakeup_events;	  /* wakeup every n events */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 812fcfc767f4..9ff9c0e37727 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2680,7 +2680,7 @@ static int _perf_event_refresh(struct perf_event *event, int refresh)
 	 * not supported on inherited events
 	 */
 	if (event->attr.inherit || event->attr.signal_on_wakeup ||
-			!is_sampling_event(event))
+			event->attr.count_sb_events || !is_sampling_event(event))
 		return -EINVAL;
 
 	atomic_add(refresh, &event->event_limit);
@@ -5956,7 +5956,7 @@ void perf_output_sample(struct perf_output_handle *handle,
 		}
 	}
 
-	if (!event->attr.watermark) {
+	if (!event->attr.count_sb_events && !event->attr.watermark) {
 		int wakeup_events = event->attr.wakeup_events;
 
 		if (wakeup_events) {
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 4e7c728569a8..f43a6081141f 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -197,6 +197,19 @@ __perf_output_begin(struct perf_output_handle *handle,
 	 * none of the data stores below can be lifted up by the compiler.
 	 */
 
+	if (event->attr.count_sb_events && !event->attr.watermark) {
+		int wakeup_events = event->attr.wakeup_events;
+
+		if (wakeup_events) {
+			int events = local_inc_return(&rb->events);
+
+			if (events >= wakeup_events) {
+				local_sub(wakeup_events, &rb->events);
+				local_inc(&rb->wakeup);
+			}
+		}
+	}
+
 	if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
 		local_add(rb->watermark, &rb->wakeup);
 
-- 
2.13.1