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Subject[PATCH 2/2] kernel/events: Add option to enable counting sideband events in wakeup_events
Date
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@linux.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
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