Re: [RFC 1/2] perf core: Add PERF_COUNT_SW_CGROUP_SWITCHES event

Peter Zijlstra
2020-12-02T16:20:46Z

On Thu, Dec 03, 2020 at 12:02:04AM +0900, Namhyung Kim wrote:

> +#ifdef CONFIG_CGROUP_PERF
> +static inline void
> +perf_sw_event_cgroup_switch(struct task_struct *prev, struct task_struct *next)
> +{
> + struct cgroup *prev_cgrp, *next_cgrp;
> +
> + rcu_read_lock();
> +
> + prev_cgrp = task_css_check(prev, perf_event_cgrp_id, 1)->cgroup;
> + next_cgrp = task_css_check(next, perf_event_cgrp_id, 1)->cgroup;
> +
> + if (prev_cgrp != next_cgrp)
> + perf_sw_event_sched(PERF_COUNT_SW_CGROUP_SWITCHES, 1, 0);
> +
> + rcu_read_unlock();
> +}
> +#else
> +static inline void perf_sw_event_cgroup_switch(struct task_struct *prev,
> + struct task_struct *next) {}
> +#endif /* CONFIG_CGROUP_PERF */
> +
> extern struct static_key_false perf_sched_events;
>
> static __always_inline bool
> @@ -1220,6 +1241,7 @@ static inline void perf_event_task_sched_out(struct task_struct *prev,
> struct task_struct *next)
> {
> perf_sw_event_sched(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 0);
> + perf_sw_event_cgroup_switch(prev, next);
>
> if (static_branch_unlikely(&perf_sched_events))
> __perf_event_task_sched_out(prev, next);

Urgh.. that's horrible, try something like this.

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 9a38f579bc76..5eb284819ee5 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1174,25 +1174,19 @@ DECLARE_PER_CPU(struct pt_regs, __perf_regs[4]);
* which is guaranteed by us not actually scheduling inside other swevents
* because those disable preemption.
*/
-static __always_inline void
-perf_sw_event_sched(u32 event_id, u64 nr, u64 addr)
+static __always_inline void __perf_sw_event_sched(u32 event_id, u64 nr, u64 addr)
{
- if (static_key_false(&perf_swevent_enabled[event_id])) {
- struct pt_regs *regs = this_cpu_ptr(&__perf_regs[0]);
+ struct pt_regs *regs = this_cpu_ptr(&__perf_regs[0]);

- perf_fetch_caller_regs(regs);
- ___perf_sw_event(event_id, nr, regs, addr);
- }
+ perf_fetch_caller_regs(regs);
+ ___perf_sw_event(event_id, nr, regs, addr);
}

extern struct static_key_false perf_sched_events;

-static __always_inline bool
-perf_sw_migrate_enabled(void)
+static __always_inline bool __perf_sw_enabled(int swevt)
{
- if (static_key_false(&perf_swevent_enabled[PERF_COUNT_SW_CPU_MIGRATIONS]))
- return true;
- return false;
+ return static_key_false(&perf_swevent_enabled[swevt]);
}

static inline void perf_event_task_migrate(struct task_struct *task)
@@ -1207,11 +1201,9 @@ static inline void perf_event_task_sched_in(struct task_struct *prev,
if (static_branch_unlikely(&perf_sched_events))
__perf_event_task_sched_in(prev, task);

- if (perf_sw_migrate_enabled() && task->sched_migrated) {
- struct pt_regs *regs = this_cpu_ptr(&__perf_regs[0]);
-
- perf_fetch_caller_regs(regs);
- ___perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, regs, 0);
+ if (__perf_sw_enabled(PERF_COUNT_SW_CPU_MIGRATIONS) &&
+ task->sched_migrated) {
+ __perf_sw_event_sched(PERF_COUNT_SW_CPU_MIGRATIONS, 1, 0);
task->sched_migrated = 0;
}
}
@@ -1219,7 +1211,13 @@ static inline void perf_event_task_sched_in(struct task_struct *prev,
static inline void perf_event_task_sched_out(struct task_struct *prev,
struct task_struct *next)
{
- perf_sw_event_sched(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 0);
+ if (__perf_sw_enabled(PERF_COUNT_SW_CONTEXT_SWITCHES))
+ __perf_sw_event_sched(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 0);
+
+ if (__perf_sw_enabled(PERF_COUNT_SW_CGROUP_SWITCHES) &&
+ (task_css_check(prev, perf_event_cgrp_id, 1)->cgroup !=
+ task_css_check(next, perf_event_cgrp_id, 1)->cgroup))
+ __perf_sw_event_sched(PERF_COUNT_SW_CGROUP_SWITCHES, 1, 0);

if (static_branch_unlikely(&perf_sched_events))
__perf_event_task_sched_out(prev, next);
@@ -1475,8 +1473,6 @@ static inline int perf_event_refresh(struct perf_event *event, int refresh)
static inline void
perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr) { }
static inline void
-perf_sw_event_sched(u32 event_id, u64 nr, u64 addr) { }
-static inline void
perf_bp_event(struct perf_event *event, void *data) { }

static inline int perf_register_guest_info_callbacks