From 9fd81dd5ce0b12341c9f83346f8d32ac68bd3841 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 19 Apr 2016 17:36:51 +0200 Subject: [PATCH] sched/fair: Optimize !CONFIG_NO_HZ_COMMON CPU load updates Some code in CPU load update only concern NO_HZ configs but it is built on all configurations. When NO_HZ isn't built, that code is harmless but just happens to take some useless ressources in CPU and memory: 1) one useless field in struct rq 2) jiffies record on every tick that is never used (cpu_load_update_periodic) 3) decay_load_missed is called two times on every tick to eventually return immediately with no action taken. And that function is dead code. For pure optimization purposes, lets conditionally build the NO_HZ related code. Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: Byungchul Park Cc: Chris Metcalf Cc: Christoph Lameter Cc: Luiz Capitulino Cc: Mike Galbraith Cc: Paul E . McKenney Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1461080211-16271-1-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 5 ++--- kernel/sched/fair.c | 9 +++++++-- kernel/sched/sched.h | 6 ++++-- 3 files changed, 13 insertions(+), 7 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c98a2688f390..71dffbb27ce6 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7381,8 +7381,6 @@ void __init sched_init(void) for (j = 0; j < CPU_LOAD_IDX_MAX; j++) rq->cpu_load[j] = 0; - rq->last_load_update_tick = jiffies; - #ifdef CONFIG_SMP rq->sd = NULL; rq->rd = NULL; @@ -7401,12 +7399,13 @@ void __init sched_init(void) rq_attach_root(rq, &def_root_domain); #ifdef CONFIG_NO_HZ_COMMON + rq->last_load_update_tick = jiffies; rq->nohz_flags = 0; #endif #ifdef CONFIG_NO_HZ_FULL rq->last_sched_tick = 0; #endif -#endif +#endif /* CONFIG_SMP */ init_rq_hrtick(rq); atomic_set(&rq->nr_iowait, 0); } diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index b70367a3e1ef..b8a33abce650 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4491,7 +4491,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) } #ifdef CONFIG_SMP - +#ifdef CONFIG_NO_HZ_COMMON /* * per rq 'load' arrray crap; XXX kill this. */ @@ -4557,6 +4557,7 @@ decay_load_missed(unsigned long load, unsigned long missed_updates, int idx) } return load; } +#endif /* CONFIG_NO_HZ_COMMON */ /** * __cpu_load_update - update the rq->cpu_load[] statistics @@ -4596,7 +4597,7 @@ decay_load_missed(unsigned long load, unsigned long missed_updates, int idx) static void cpu_load_update(struct rq *this_rq, unsigned long this_load, unsigned long pending_updates) { - unsigned long tickless_load = this_rq->cpu_load[0]; + unsigned long __maybe_unused tickless_load = this_rq->cpu_load[0]; int i, scale; this_rq->nr_load_updates++; @@ -4609,6 +4610,7 @@ static void cpu_load_update(struct rq *this_rq, unsigned long this_load, /* scale is effectively 1 << i now, and >> i divides by scale */ old_load = this_rq->cpu_load[i]; +#ifdef CONFIG_NO_HZ_COMMON old_load = decay_load_missed(old_load, pending_updates - 1, i); if (tickless_load) { old_load -= decay_load_missed(tickless_load, pending_updates - 1, i); @@ -4619,6 +4621,7 @@ static void cpu_load_update(struct rq *this_rq, unsigned long this_load, */ old_load += tickless_load; } +#endif new_load = this_load; /* * Round up the averaging division if load is increasing. This @@ -4731,8 +4734,10 @@ static inline void cpu_load_update_nohz(struct rq *this_rq, static void cpu_load_update_periodic(struct rq *this_rq, unsigned long load) { +#ifdef CONFIG_NO_HZ_COMMON /* See the mess around cpu_load_update_nohz(). */ this_rq->last_load_update_tick = READ_ONCE(jiffies); +#endif cpu_load_update(this_rq, load, 1); } diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 32d9e22cfacf..69da6fcaa0e8 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -585,11 +585,13 @@ struct rq { #endif #define CPU_LOAD_IDX_MAX 5 unsigned long cpu_load[CPU_LOAD_IDX_MAX]; - unsigned long last_load_update_tick; #ifdef CONFIG_NO_HZ_COMMON +#ifdef CONFIG_SMP + unsigned long last_load_update_tick; +#endif /* CONFIG_SMP */ u64 nohz_stamp; unsigned long nohz_flags; -#endif +#endif /* CONFIG_NO_HZ_COMMON */ #ifdef CONFIG_NO_HZ_FULL unsigned long last_sched_tick; #endif