linux-kernel - Re: [PATCH v2] sched/core: forced idle accounting

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Date:   Wed, 10 Nov 2021 09:59:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Don <joshdon@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Vineeth Pillai <vineethrp@...il.com>,
        Hao Luo <haoluo@...gle.com>, Tao Zhou <tao.zhou@...ux.dev>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched/core: forced idle accounting

On Wed, Nov 10, 2021 at 09:38:53AM +0100, Peter Zijlstra wrote:
> On Tue, Nov 09, 2021 at 02:59:00PM -0800, Josh Don wrote:
> > On Tue, Nov 9, 2021 at 3:15 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > On Mon, Oct 18, 2021 at 01:34:28PM -0700, Josh Don wrote:
> > > > @@ -5804,6 +5830,12 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> > > >               }
> > > >       }
> > > >
> > > > +     if (rq->core->core_forceidle_count) {
> > >
> > > Does this want to be something like:
> > >
> > >         if (schedstat_enabled() && .. ) ?
> > >
> > > afaict without schedstat on this is dead code.
> > >
> > 
> > Makes sense to me, and similarly we can bail out of sched_core_tick()
> > early in the disabled case.
> 
> Ok, I already changed the patch to include the above, lemme also edit
> sched_core_tick().


Something like so then?

--- a/kernel/sched/core_sched.c
+++ b/kernel/sched/core_sched.c
@@ -235,7 +235,7 @@ int sched_core_share_pid(unsigned int cm
 #ifdef CONFIG_SCHEDSTATS
 
 /* REQUIRES: rq->core's clock recently updated. */
-void sched_core_account_forceidle(struct rq *rq)
+void __sched_core_account_forceidle(struct rq *rq)
 {
 	const struct cpumask *smt_mask = cpu_smt_mask(cpu_of(rq));
 	u64 delta, now = rq_clock(rq->core);
@@ -256,9 +256,6 @@ void sched_core_account_forceidle(struct
 
 	rq->core->core_forceidle_start = now;
 
-	if (!schedstat_enabled())
-		return;
-
 	if (WARN_ON_ONCE(!rq->core->core_forceidle_occupation)) {
 		/* can't be forced idle without a running task */
 	} else if (rq->core->core_forceidle_count > 1 ||
@@ -283,17 +280,15 @@ void sched_core_account_forceidle(struct
 	}
 }
 
-void sched_core_tick(struct rq *rq)
+void __sched_core_tick(struct rq *rq)
 {
-	if (!sched_core_enabled(rq))
-		return;
-
 	if (!rq->core->core_forceidle_count)
 		return;
 
 	if (rq != rq->core)
 		update_rq_clock(rq->core);
-	sched_core_account_forceidle(rq);
+
+	__sched_core_account_forceidle(rq);
 }
 
 #endif /* CONFIG_SCHEDSTATS */
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1304,20 +1304,6 @@ static inline bool sched_group_cookie_ma
 }
 #endif /* CONFIG_SCHED_CORE */
 
-#if defined(CONFIG_SCHED_CORE) && defined(CONFIG_SCHEDSTATS)
-
-extern void sched_core_account_forceidle(struct rq *rq);
-
-extern void sched_core_tick(struct rq *rq);
-
-#else
-
-static inline void sched_core_account_forceidle(struct rq *rq) {}
-
-static inline void sched_core_tick(struct rq *rq) {}
-
-#endif /* CONFIG_SCHED_CORE && CONFIG_SCHEDSTATS */
-
 static inline void lockdep_assert_rq_held(struct rq *rq)
 {
 	lockdep_assert_held(__rq_lockp(rq));
@@ -1870,6 +1856,32 @@ static inline void flush_smp_call_functi
 #include "stats.h"
 #include "autogroup.h"
 
+#if defined(CONFIG_SCHED_CORE) && defined(CONFIG_SCHEDSTATS)
+
+extern void __sched_core_account_forceidle(struct rq *rq);
+
+static inline void sched_core_account_forceidle(struct rq *rq)
+{
+	if (schedstat_enabled())
+		__sched_core_account_forceidle(rq);
+}
+
+extern void __sched_core_tick(struct rq *rq);
+
+static inline void sched_core_tick(struct rq *rq)
+{
+	if (sched_core_enabled(rq) && schedstat_enabled())
+		__sched_core_tick(rq);
+}
+
+#else
+
+static inline void sched_core_account_forceidle(struct rq *rq) {}
+
+static inline void sched_core_tick(struct rq *rq) {}
+
+#endif /* CONFIG_SCHED_CORE && CONFIG_SCHEDSTATS */
+
 #ifdef CONFIG_CGROUP_SCHED
 
 /*