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@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210210083327.22726-2-namhyung@kernel.org

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 92d51a7beaeaf9a3bc53612fbd8914a08ddd762e..8989b2b7268d5ee584a6bb969d6751855331b36b 100644 (file)
--- 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 31b00e3b69c9c25c429d778def87940b3c599043..0b58970bab6b9bd157090123ab42ecaca837847f 100644 (file)
--- 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 */
 };