[tip: perf/core] perf core: Add PERF_COUNT_SW_CGROUP_SWITCHES event

[tip-bot2 for Namhyung Kim]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     a389ea9c161d142bf11fd4c553988c2daa9f5404
Gitweb:        https://git.kernel.org/tip/a389ea9c161d142bf11fd4c553988c2daa9f5404
Author:        Namhyung Kim <namhyung@xxxxxxxxxx>
AuthorDate:    Wed, 10 Feb 2021 17:33:26 +09:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 16 Apr 2021 16:32:43 +02:00

perf core: Add PERF_COUNT_SW_CGROUP_SWITCHES event

This patch adds a new software event to count context switches
involving cgroup switches.  So it's counted only if cgroups of
previous and next tasks are different.  Note that it only checks the
cgroups in the perf_event subsystem.  For cgroup v2, it shouldn't
matter anyway.

One can argue that we can do this by using existing sched_switch event
with eBPF.  But some systems might not have eBPF for some reason so
I'd like to add this as a simple way.

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210210083327.22726-2-namhyung@xxxxxxxxxx
---
 include/linux/perf_event.h      | 7 +++++++
 include/uapi/linux/perf_event.h | 1 +
 2 files changed, 8 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 92d51a7..8989b2b 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1218,6 +1218,13 @@ static inline void perf_event_task_sched_out(struct task_struct *prev,
 	if (__perf_sw_enabled(PERF_COUNT_SW_CONTEXT_SWITCHES))
 		__perf_sw_event_sched(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 0);
 
+#ifdef CONFIG_CGROUP_PERF
+	if (__perf_sw_enabled(PERF_COUNT_SW_CGROUP_SWITCHES) &&
+	    perf_cgroup_from_task(prev, NULL) !=
+	    perf_cgroup_from_task(next, NULL))
+		__perf_sw_event_sched(PERF_COUNT_SW_CGROUP_SWITCHES, 1, 0);
+#endif
+
 	if (static_branch_unlikely(&perf_sched_events))
 		__perf_event_task_sched_out(prev, next);
 }
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 31b00e3..0b58970 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -112,6 +112,7 @@ enum perf_sw_ids {
 	PERF_COUNT_SW_EMULATION_FAULTS		= 8,
 	PERF_COUNT_SW_DUMMY			= 9,
 	PERF_COUNT_SW_BPF_OUTPUT		= 10,
+	PERF_COUNT_SW_CGROUP_SWITCHES		= 11,
 
 	PERF_COUNT_SW_MAX,			/* non-ABI */
 };