linux-kernel - Re: [PATCH v3 1/3] perf core: Factor out __perf_sw_event

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Date:   Thu, 25 Feb 2021 01:00:08 -0800
From:   Stephane Eranian <eranian@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCH v3 1/3] perf core: Factor out __perf_sw_event_sched

Hi Peter,

Any comments on this patch series?

It is quite useful to be able to count the number of cgroup switches
simply using perf stat/record.
Not all context switches (cs) are necessarily cgroup switches.
Thanks.

On Wed, Feb 10, 2021 at 12:33 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> In some cases, we need to check more than whether the software event
> is enabled.  So split the condition check and the actual event
> handling.  This is a preparation for the next change.
>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  include/linux/perf_event.h | 33 ++++++++++++---------------------
>  1 file changed, 12 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index fab42cfbd350..2a1be6026a2f 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1174,30 +1174,24 @@ 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)
>  {
> -       if (perf_sw_migrate_enabled())
> +       if (__perf_sw_enabled(PERF_COUNT_SW_CPU_MIGRATIONS))
>                 task->sched_migrated = 1;
>  }
>
> @@ -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 +1211,8 @@ 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 (static_branch_unlikely(&perf_sched_events))
>                 __perf_event_task_sched_out(prev, next);
> @@ -1475,8 +1468,6 @@ 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
> --
> 2.30.0.478.g8a0d178c01-goog
>