[PATCHv2] sched: Replace nr_iowait_cpu() with a bool accessor

[Christian Loehle]

The menu governor was the last consumer of the per-CPU I/O-wait count
that needed its magnitude, apart from nr_iowait() summing it globally.
Commit 38f83090f515 ("cpuidle: menu: Remove iowait influence") removed
that use. All remaining per-CPU consumers only test for zero/nonzero.

Replace nr_iowait_cpu() with bool cpu_has_iowait() and update the generic
and s390 idle accounting callers. Have nr_iowait() read the counters
directly so that the global total and existing accounting are preserved.
Replace the stale menu comment with a description of the predicate.

The conversion was done with coccinelle:

@ predicate depends on patch @
expression cpu;
@@

- nr_iowait_cpu(cpu) > 0
+ cpu_has_iowait(cpu)

@ callers depends on patch @
expression cpu;
@@

- nr_iowait_cpu(cpu)
+ cpu_has_iowait(cpu)

Signed-off-by: Christian Loehle <christian.loehle@xxxxxxx>
---
v2: Move the cocci excerpt to the commit message (Peter)


 arch/s390/kernel/idle.c    |  4 ++--
 include/linux/sched/stat.h |  2 +-
 kernel/sched/core.c        | 13 +++++--------
 kernel/sched/cputime.c     | 10 +++++-----
 4 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c
index dd12efb58201..ff9732ef494c 100644
--- a/arch/s390/kernel/idle.c
+++ b/arch/s390/kernel/idle.c
@@ -82,13 +82,13 @@ static u64 arch_cpu_idle_time(int cpu, enum cpu_usage_stat idx, bool compute_del
 
 u64 arch_kcpustat_field_idle(int cpu)
 {
-	return arch_cpu_idle_time(cpu, CPUTIME_IDLE, !nr_iowait_cpu(cpu));
+	return arch_cpu_idle_time(cpu, CPUTIME_IDLE, !cpu_has_iowait(cpu));
 }
 EXPORT_SYMBOL_GPL(arch_kcpustat_field_idle);
 
 u64 arch_kcpustat_field_iowait(int cpu)
 {
-	return arch_cpu_idle_time(cpu, CPUTIME_IOWAIT, nr_iowait_cpu(cpu));
+	return arch_cpu_idle_time(cpu, CPUTIME_IOWAIT, cpu_has_iowait(cpu));
 }
 EXPORT_SYMBOL_GPL(arch_kcpustat_field_iowait);
 
diff --git a/include/linux/sched/stat.h b/include/linux/sched/stat.h
index 0108a38bb64d..4810b14d0372 100644
--- a/include/linux/sched/stat.h
+++ b/include/linux/sched/stat.h
@@ -20,7 +20,7 @@ extern int nr_processes(void);
 extern unsigned int nr_running(void);
 extern bool single_task_running(void);
 extern unsigned int nr_iowait(void);
-extern unsigned int nr_iowait_cpu(int cpu);
+extern bool cpu_has_iowait(int cpu);
 
 static inline int sched_info_on(void)
 {
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1fe40de6ebe3..1bde5187dafd 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5588,15 +5588,12 @@ unsigned long long nr_context_switches(void)
 }
 
 /*
- * Consumers of these two interfaces, like for example the cpuidle menu
- * governor, are using nonsensical data. Preferring shallow idle state selection
- * for a CPU that has IO-wait which might not even end up running the task when
- * it does become runnable.
+ * Return whether any tasks are accounted as I/O waiters on this CPU.
+ * They may wake up on a different CPU.
  */
-
-unsigned int nr_iowait_cpu(int cpu)
+bool cpu_has_iowait(int cpu)
 {
-	return atomic_read(&cpu_rq(cpu)->nr_iowait);
+	return atomic_read(&cpu_rq(cpu)->nr_iowait) != 0;
 }
 
 /*
@@ -5634,7 +5631,7 @@ unsigned int nr_iowait(void)
 	unsigned int i, sum = 0;
 
 	for_each_possible_cpu(i)
-		sum += nr_iowait_cpu(i);
+		sum += atomic_read(&cpu_rq(i)->nr_iowait);
 
 	return sum;
 }
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 06bddaa738e5..1f84a950abed 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -431,7 +431,7 @@ static void kcpustat_idle_stop(struct kernel_cpustat *kc, u64 now)
 	if (!kc->idle_elapse)
 		return;
 
-	iowait = nr_iowait_cpu(smp_processor_id()) > 0;
+	iowait = cpu_has_iowait(smp_processor_id());
 	delta = now - kc->idle_entrytime;
 	steal = steal_account_process_time(delta);
 
@@ -544,14 +544,14 @@ static u64 kcpustat_field_dyntick(int cpu, enum cpu_usage_stat idx,
 u64 kcpustat_field_idle(int cpu)
 {
 	return kcpustat_field_dyntick(cpu, CPUTIME_IDLE,
-				      !nr_iowait_cpu(cpu), ktime_get());
+				      !cpu_has_iowait(cpu), ktime_get());
 }
 EXPORT_SYMBOL_GPL(kcpustat_field_idle);
 
 u64 kcpustat_field_iowait(int cpu)
 {
 	return kcpustat_field_dyntick(cpu, CPUTIME_IOWAIT,
-				      nr_iowait_cpu(cpu), ktime_get());
+				      cpu_has_iowait(cpu), ktime_get());
 }
 EXPORT_SYMBOL_GPL(kcpustat_field_iowait);
 #else
@@ -601,7 +601,7 @@ static u64 get_cpu_sleep_time_us(int cpu, enum cpu_usage_stat idx,
 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
 {
 	return get_cpu_sleep_time_us(cpu, CPUTIME_IDLE,
-				     !nr_iowait_cpu(cpu), last_update_time);
+				     !cpu_has_iowait(cpu), last_update_time);
 }
 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
 
@@ -625,7 +625,7 @@ EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
 {
 	return get_cpu_sleep_time_us(cpu, CPUTIME_IOWAIT,
-				     nr_iowait_cpu(cpu), last_update_time);
+				     cpu_has_iowait(cpu), last_update_time);
 }
 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
 
-- 
2.34.1