[PATCH v1 1/3] perf/core: store context switch out type into Perf trace

From: Alexey Budankov
Date: Mon Mar 05 2018 - 06:37:12 EST



Store thread context-switch-out event type into Perf trace as a part of
PERF_RECORD_SWITCH[_CPU_WIDE] records.

Introduced types of switch-out events assumed to be
a) preempt: task->state == TASK_RUNNING and b) yield: !preempt;

New yield event type is encoded using special
PERF_RECORD_MISC_SWITCH_OUT_YIELD bit extending PERF_RECORD_MISC_SWITCH_OUT
meaning traditional preemption switch out event:

misc &= PERF_RECORD_MISC_SWITCH_OUT | PERF_RECORD_MISC_SWITCH_OUT_YIELD

Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
---
include/uapi/linux/perf_event.h | 5 +++++
kernel/events/core.c | 4 +++-
2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 6f873503552d..0339c829cda5 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -654,6 +654,11 @@ struct perf_event_mmap_page {
* perf_event_attr::precise_ip.
*/
#define PERF_RECORD_MISC_EXACT_IP (1 << 14)
+/*
+ * Indicates that thread explicitly yielded cpu due to
+ * a call of some synchronization API e.g. futex system call
+ */
+#define PERF_RECORD_MISC_SWITCH_OUT_YIELD (1 << 14)
/*
* Reserve the last bit to indicate some extended misc field
*/
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 57898102847f..1faa6dde090c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7216,6 +7216,8 @@ static void perf_event_switch(struct task_struct *task,
struct task_struct *next_prev, bool sched_in)
{
struct perf_switch_event switch_event;
+ __u16 switch_type = sched_in ? 0 : PERF_RECORD_MISC_SWITCH_OUT |
+ (task->state == TASK_RUNNING ? 0 : PERF_RECORD_MISC_SWITCH_OUT_YIELD);

/* N.B. caller checks nr_switch_events != 0 */

@@ -7225,7 +7227,7 @@ static void perf_event_switch(struct task_struct *task,
.event_id = {
.header = {
/* .type */
- .misc = sched_in ? 0 : PERF_RECORD_MISC_SWITCH_OUT,
+ .misc = switch_type,
/* .size */
},
/* .next_prev_pid */