Commit b0c79224 authored Jun 03, 2019 by Valentin Schneider Committed by Ingo Molnar Jun 17, 2019

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>

parent e3b929b0

kernel/sched/fair.c

+16 −10

Original line number	Diff line number	Diff line
		@@ -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);
		}