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Message-ID: <CAM9d7cgbQ6vQTu76NqZdE33-+LuMMJw4YdoSy5uOv49hm0Rrog@mail.gmail.com>
Date: Thu, 21 Jan 2021 17:00:18 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: 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>,
Stephane Eranian <eranian@...gle.com>,
Andi Kleen <ak@...ux.intel.com>,
Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCH 1/2] perf core: Add PERF_COUNT_SW_CGROUP_SWITCHES event
Hi Peter,
Can you please take a look at this again?
Thanks,
Namhyung
On Thu, Jan 14, 2021 at 5:50 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> 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.
>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> include/linux/perf_event.h | 38 +++++++++++++++------------------
> include/uapi/linux/perf_event.h | 1 +
> 2 files changed, 18 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 9a38f579bc76..304ef42d42d1 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 +1211,13 @@ 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
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index b15e3447cd9f..16b9538ad89b 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 */
> };
> --
> 2.30.0.284.gd98b1dd5eaa7-goog
>
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