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From: Peter Zijlstra <peterz@infradead.org>
To: tglx@linutronix.de, mingo@kernel.org, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	bristot@redhat.com, bsingharora@gmail.com, pbonzini@redhat.com,
	maz@kernel.org
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	peterz@infradead.org, riel@surriel.com, hannes@cmpxchg.org
Subject: [PATCH 3/6] sched: Simplify sched_info_on()
Date: Wed, 05 May 2021 12:59:43 +0200	[thread overview]
Message-ID: <20210505111525.121458839@infradead.org> (raw)
In-Reply-To: <20210505105940.190490250@infradead.org>

The situation around sched_info is somewhat complicated, it is used by
sched_stats and delayacct and, indirectly, kvm.

If SCHEDSTATS=Y (but disabled by default) sched_info_on() is
unconditionally true -- this is the case for all distro kernel configs
I checked.

If for some reason SCHEDSTATS=N, but TASK_DELAY_ACCT=Y, then
sched_info_on() can return false when delayacct is disabled,
presumably because there would be no other users left; except kvm is.

Instead of complicating matters further by accurately accounting
sched_stat and kvm state, simply unconditionally enable when
SCHED_INFO=Y, matching the common distro case.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/sched/stat.h |   10 ++--------
 kernel/delayacct.c         |    1 -
 kernel/sched/stats.h       |   37 ++++++++++---------------------------
 3 files changed, 12 insertions(+), 36 deletions(-)

--- a/include/linux/sched/stat.h
+++ b/include/linux/sched/stat.h
@@ -3,6 +3,7 @@
 #define _LINUX_SCHED_STAT_H
 
 #include <linux/percpu.h>
+#include <linux/kconfig.h>
 
 /*
  * Various counters maintained by the scheduler and fork(),
@@ -23,14 +24,7 @@ extern unsigned long nr_iowait_cpu(int c
 
 static inline int sched_info_on(void)
 {
-#ifdef CONFIG_SCHEDSTATS
-	return 1;
-#elif defined(CONFIG_TASK_DELAY_ACCT)
-	extern int delayacct_on;
-	return delayacct_on;
-#else
-	return 0;
-#endif
+	return IS_ENABLED(CONFIG_SCHED_INFO);
 }
 
 #ifdef CONFIG_SCHEDSTATS
--- a/kernel/delayacct.c
+++ b/kernel/delayacct.c
@@ -15,7 +15,6 @@
 #include <linux/module.h>
 
 int delayacct_on __read_mostly = 1;	/* Delay accounting turned on/off */
-EXPORT_SYMBOL_GPL(delayacct_on);
 struct kmem_cache *delayacct_cache;
 
 static int __init delayacct_setup_disable(char *str)
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -150,11 +150,6 @@ static inline void psi_sched_switch(stru
 #endif /* CONFIG_PSI */
 
 #ifdef CONFIG_SCHED_INFO
-static inline void sched_info_reset_dequeued(struct task_struct *t)
-{
-	t->sched_info.last_queued = 0;
-}
-
 /*
  * We are interested in knowing how long it was from the *first* time a
  * task was queued to the time that it finally hit a CPU, we call this routine
@@ -163,13 +158,12 @@ static inline void sched_info_reset_dequ
  */
 static inline void sched_info_dequeue(struct rq *rq, struct task_struct *t)
 {
-	unsigned long long now = rq_clock(rq), delta = 0;
+	unsigned long long delta = 0;
 
-	if (sched_info_on()) {
-		if (t->sched_info.last_queued)
-			delta = now - t->sched_info.last_queued;
+	if (t->sched_info.last_queued) {
+		delta = rq_clock(rq) - t->sched_info.last_queued;
+		t->sched_info.last_queued = 0;
 	}
-	sched_info_reset_dequeued(t);
 	t->sched_info.run_delay += delta;
 
 	rq_sched_info_dequeue(rq, delta);
@@ -184,9 +178,10 @@ static void sched_info_arrive(struct rq
 {
 	unsigned long long now = rq_clock(rq), delta = 0;
 
-	if (t->sched_info.last_queued)
+	if (t->sched_info.last_queued) {
 		delta = now - t->sched_info.last_queued;
-	sched_info_reset_dequeued(t);
+		t->sched_info.last_queued = 0;
+	}
 	t->sched_info.run_delay += delta;
 	t->sched_info.last_arrival = now;
 	t->sched_info.pcount++;
@@ -201,10 +196,8 @@ static void sched_info_arrive(struct rq
  */
 static inline void sched_info_enqueue(struct rq *rq, struct task_struct *t)
 {
-	if (sched_info_on()) {
-		if (!t->sched_info.last_queued)
-			t->sched_info.last_queued = rq_clock(rq);
-	}
+	if (!t->sched_info.last_queued)
+		t->sched_info.last_queued = rq_clock(rq);
 }
 
 /*
@@ -231,7 +224,7 @@ static inline void sched_info_depart(str
  * the idle task.)  We are only called when prev != next.
  */
 static inline void
-__sched_info_switch(struct rq *rq, struct task_struct *prev, struct task_struct *next)
+sched_info_switch(struct rq *rq, struct task_struct *prev, struct task_struct *next)
 {
 	/*
 	 * prev now departs the CPU.  It's not interesting to record
@@ -245,18 +238,8 @@ __sched_info_switch(struct rq *rq, struc
 		sched_info_arrive(rq, next);
 }
 
-static inline void
-sched_info_switch(struct rq *rq, struct task_struct *prev, struct task_struct *next)
-{
-	if (sched_info_on())
-		__sched_info_switch(rq, prev, next);
-}
-
 #else /* !CONFIG_SCHED_INFO: */
 # define sched_info_enqueue(rq, t)	do { } while (0)
-# define sched_info_reset_dequeued(t)	do { } while (0)
 # define sched_info_dequeue(rq, t)	do { } while (0)
-# define sched_info_depart(rq, t)	do { } while (0)
-# define sched_info_arrive(rq, next)	do { } while (0)
 # define sched_info_switch(rq, t, next)	do { } while (0)
 #endif /* CONFIG_SCHED_INFO */



  parent reply	other threads:[~2021-05-05 11:18 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-05 10:59 [PATCH 0/6] sched,delayacct: Some cleanups Peter Zijlstra
2021-05-05 10:59 ` [PATCH 1/6] delayacct: Use sched_clock() Peter Zijlstra
2021-05-05 14:40   ` Rik van Riel
2021-05-06 13:59   ` Johannes Weiner
2021-05-06 14:17     ` Peter Zijlstra
2021-05-06 15:17       ` Johannes Weiner
2021-05-07 12:40   ` Balbir Singh
2021-05-12 10:43   ` Mel Gorman
2021-05-05 10:59 ` [PATCH 2/6] sched: Rename sched_info_{queued,dequeued} Peter Zijlstra
2021-05-05 14:39   ` Rik van Riel
2021-05-06 13:59   ` Johannes Weiner
2021-05-10  8:45   ` Balbir Singh
2021-05-12 10:49   ` Mel Gorman
2021-05-05 10:59 ` Peter Zijlstra [this message]
2021-05-06 14:03   ` [PATCH 3/6] sched: Simplify sched_info_on() Johannes Weiner
2021-05-12 11:10   ` Mel Gorman
2021-05-12 11:32     ` Peter Zijlstra
2021-05-12 12:51       ` Mel Gorman
2021-05-05 10:59 ` [PATCH 4/6] kvm: Select SCHED_INFO instead of TASK_DELAY_ACCT Peter Zijlstra
2021-05-05 11:37   ` Paolo Bonzini
2021-05-06 14:38   ` Marc Zyngier
2021-05-07 12:42   ` Balbir Singh
2021-05-12 11:11   ` Mel Gorman
2021-05-05 10:59 ` [PATCH 5/6] delayacct: Add static_branch in scheduler hooks Peter Zijlstra
2021-05-06 14:05   ` Johannes Weiner
2021-05-10  8:42   ` Balbir Singh
2021-05-12 11:13   ` Mel Gorman
2021-05-05 10:59 ` [PATCH 6/6] [RFC] delayacct: Default disabled Peter Zijlstra
2021-05-12 11:35   ` Mel Gorman
2021-05-05 22:29 ` [PATCH 0/6] sched,delayacct: Some cleanups Balbir Singh
2021-05-06  9:13   ` Peter Zijlstra
2021-05-07 12:38     ` Balbir Singh
2021-05-12 11:34       ` Mel Gorman
2021-05-12 11:38         ` Peter Zijlstra
2021-05-12 12:23         ` Paul Wise
2021-05-12 13:00           ` Mel Gorman
2021-05-13  1:29             ` Paul Wise
2021-06-25  0:50         ` Paul Wise
2021-05-07  9:05 ` Thomas Gleixner
2021-05-10  7:08 ` Ingo Molnar
2021-05-10 12:05 ` [PATCH 7/6] delayacct: Add sysctl to enable at runtime Peter Zijlstra
2021-05-10 12:06   ` Peter Zijlstra
2021-05-12 11:40   ` Mel Gorman

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