Messages in this thread Patch in this message | | | Date | Mon, 11 Nov 2019 09:32:35 -0000 | From | "tip-bot2 for Peter Zijlstra" <> | Subject | [tip: sched/core] sched/core: Optimize pick_next_task() |
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The following commit has been merged into the sched/core branch of tip:
Commit-ID: 5d7d605642b28a5911198a405a6072f091bfbee6 Gitweb: https://git.kernel.org/tip/5d7d605642b28a5911198a405a6072f091bfbee6 Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Fri, 08 Nov 2019 14:15:57 +01:00 Committer: Ingo Molnar <mingo@kernel.org> CommitterDate: Mon, 11 Nov 2019 08:35:19 +01:00
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) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> 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 <mingo@kernel.org> --- 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 59c4f29..7cf6547 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 c48a695..da81451 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 179d1d4..0fdceac 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 c8870c5..66172a3 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);
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