sched/fair: Clean up definition of NOHZ blocked load functions

cfs_rq_has_blocked() and others_have_blocked() are only used within
update_blocked_averages(). The !CONFIG_FAIR_GROUP_SCHED version of the
latter calls them within a #define CONFIG_NO_HZ_COMMON block, whereas
the CONFIG_FAIR_GROUP_SCHED one calls them unconditionnally.

As reported by Qian, the above leads to this warning in
!CONFIG_NO_HZ_COMMON configs:

  kernel/sched/fair.c: In function 'update_blocked_averages':
  kernel/sched/fair.c:7750:7: warning: variable 'done' set but not used [-Wunused-but-set-variable]

It wouldn't be wrong to keep cfs_rq_has_blocked() and
others_have_blocked() as they are, but since their only current use is
to figure out when we can stop calling update_blocked_averages() on
fully decayed NOHZ idle CPUs, we can give them a new definition for
!CONFIG_NO_HZ_COMMON.

Change the definition of cfs_rq_has_blocked() and
others_have_blocked() for !CONFIG_NO_HZ_COMMON so that the
NOHZ-specific blocks of update_blocked_averages() become no-ops and
the 'done' variable gets optimised out.

While at it, remove the CONFIG_NO_HZ_COMMON block from the
!CONFIG_FAIR_GROUP_SCHED definition of update_blocked_averages() by
using the newly-introduced update_blocked_load_status() helper.

No change in functionality intended.

[ Additions by Peter Zijlstra. ]

Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190603115424.7951-1-valentin.schneider@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7f8d477f90fec636bc16d1927b01ef731ffbf847..4c8f45ed093c9a5dfda027ff014d5981ccdfde8d 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7393,6 +7393,7 @@ static void attach_tasks(struct lb_env *env)
        rq_unlock(env->dst_rq, &rf);
 }
 
+#ifdef CONFIG_NO_HZ_COMMON
 static inline bool cfs_rq_has_blocked(struct cfs_rq *cfs_rq)
 {
        if (cfs_rq->avg.load_avg)
@@ -7420,6 +7421,19 @@ static inline bool others_have_blocked(struct rq *rq)
        return false;
 }
 
+static inline void update_blocked_load_status(struct rq *rq, bool has_blocked)
+{
+       rq->last_blocked_load_update_tick = jiffies;
+
+       if (!has_blocked)
+               rq->has_blocked_load = 0;
+}
+#else
+static inline bool cfs_rq_has_blocked(struct cfs_rq *cfs_rq) { return false; }
+static inline bool others_have_blocked(struct rq *rq) { return false; }
+static inline void update_blocked_load_status(struct rq *rq, bool has_blocked) {}
+#endif
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
 
 static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
@@ -7485,11 +7499,7 @@ static void update_blocked_averages(int cpu)
        if (others_have_blocked(rq))
                done = false;
 
-#ifdef CONFIG_NO_HZ_COMMON
-       rq->last_blocked_load_update_tick = jiffies;
-       if (done)
-               rq->has_blocked_load = 0;
-#endif
+       update_blocked_load_status(rq, !done);
        rq_unlock_irqrestore(rq, &rf);
 }
 
@@ -7555,11 +7565,7 @@ static inline void update_blocked_averages(int cpu)
        update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
        update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
        update_irq_load_avg(rq, 0);
-#ifdef CONFIG_NO_HZ_COMMON
-       rq->last_blocked_load_update_tick = jiffies;
-       if (!cfs_rq_has_blocked(cfs_rq) && !others_have_blocked(rq))
-               rq->has_blocked_load = 0;
-#endif
+       update_blocked_load_status(rq, cfs_rq_has_blocked(cfs_rq) || others_have_blocked(rq));
        rq_unlock_irqrestore(rq, &rf);
 }