From 5d7d605642b28a5911198a405a6072f091bfbee6 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 8 Nov 2019 14:15:57 +0100 Subject: [PATCH] sched/core: Optimize pick_next_task() Ever since we moved the sched_class definitions into their own files, the constant expression {fair,idle}_sched_class.pick_next_task() is not in fact a compile time constant anymore and results in an indirect call (barring LTO). Fix that by exposing pick_next_task_{fair,idle}() directly, this gets rid of the indirect call (and RETPOLINE) on the fast path. Also remove the unlikely() from the idle case, it is in fact /the/ way we select idle -- and that is a very common thing to do. Performance for will-it-scale/sched_yield improves by 2% (as reported by 0-day). Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: bsegall@google.com Cc: dietmar.eggemann@arm.com Cc: juri.lelli@redhat.com Cc: ktkhai@virtuozzo.com Cc: mgorman@suse.de Cc: qais.yousef@arm.com Cc: qperret@google.com Cc: rostedt@goodmis.org Cc: valentin.schneider@arm.com Cc: vincent.guittot@linaro.org Link: https://lkml.kernel.org/r/20191108131909.603037345@infradead.org Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 6 +++--- kernel/sched/fair.c | 2 +- kernel/sched/idle.c | 2 +- kernel/sched/sched.h | 3 +++ 4 files changed, 8 insertions(+), 5 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 59c4f2963417..7cf65474fa26 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3917,14 +3917,14 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) prev->sched_class == &fair_sched_class) && rq->nr_running == rq->cfs.h_nr_running)) { - p = fair_sched_class.pick_next_task(rq, prev, rf); + p = pick_next_task_fair(rq, prev, rf); if (unlikely(p == RETRY_TASK)) goto restart; /* Assumes fair_sched_class->next == idle_sched_class */ - if (unlikely(!p)) { + if (!p) { put_prev_task(rq, prev); - p = idle_sched_class.pick_next_task(rq, NULL, NULL); + p = pick_next_task_idle(rq, NULL, NULL); } return p; diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c48a695a140c..da81451d5575 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6611,7 +6611,7 @@ preempt: set_last_buddy(se); } -static struct task_struct * +struct task_struct * pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) { struct cfs_rq *cfs_rq = &rq->cfs; diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 179d1d4ac5a6..0fdceac00b70 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -391,7 +391,7 @@ static void set_next_task_idle(struct rq *rq, struct task_struct *next) schedstat_inc(rq->sched_goidle); } -static struct task_struct * +struct task_struct * pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) { struct task_struct *next = rq->idle; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index c8870c5bd7df..66172a337675 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1821,6 +1821,9 @@ static inline bool sched_fair_runnable(struct rq *rq) return rq->cfs.nr_running > 0; } +extern struct task_struct *pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf); +extern struct task_struct *pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf); + #ifdef CONFIG_SMP extern void update_group_capacity(struct sched_domain *sd, int cpu); -- 2.30.2