From a0e813f26ebcb25c0b5e504498fbd796cca1a4ba Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 8 Nov 2019 14:16:00 +0100 Subject: [PATCH] sched/core: Further clarify sched_class::set_next_task() It turns out there really is something special to the first set_next_task() invocation. In specific the 'change' pattern really should not cause balance callbacks. 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 Fixes: f95d4eaee6d0 ("sched/{rt,deadline}: Fix set_next_task vs pick_next_task") Link: https://lkml.kernel.org/r/20191108131909.775434698@infradead.org Signed-off-by: Ingo Molnar --- kernel/sched/deadline.c | 7 +++++-- kernel/sched/fair.c | 2 +- kernel/sched/idle.c | 4 ++-- kernel/sched/rt.c | 7 +++++-- kernel/sched/sched.h | 4 ++-- kernel/sched/stop_task.c | 4 ++-- 6 files changed, 17 insertions(+), 11 deletions(-) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index f7fbb4427959..43323f875cb9 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1743,13 +1743,16 @@ static void start_hrtick_dl(struct rq *rq, struct task_struct *p) } #endif -static void set_next_task_dl(struct rq *rq, struct task_struct *p) +static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first) { p->se.exec_start = rq_clock_task(rq); /* You can't push away the running task */ dequeue_pushable_dl_task(rq, p); + if (!first) + return; + if (hrtick_enabled(rq)) start_hrtick_dl(rq, p); @@ -1782,7 +1785,7 @@ static struct task_struct *pick_next_task_dl(struct rq *rq) dl_se = pick_next_dl_entity(rq, dl_rq); BUG_ON(!dl_se); p = dl_task_of(dl_se); - set_next_task_dl(rq, p); + set_next_task_dl(rq, p, true); return p; } diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index ba97d1a1b976..81eba554db8d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10344,7 +10344,7 @@ static void switched_to_fair(struct rq *rq, struct task_struct *p) * This routine is mostly called to set cfs_rq->curr field when a task * migrates between groups/classes. */ -static void set_next_task_fair(struct rq *rq, struct task_struct *p) +static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first) { struct sched_entity *se = &p->se; diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index f88b79eeee1e..428cd05c0b5d 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -385,7 +385,7 @@ static void put_prev_task_idle(struct rq *rq, struct task_struct *prev) { } -static void set_next_task_idle(struct rq *rq, struct task_struct *next) +static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first) { update_idle_core(rq); schedstat_inc(rq->sched_goidle); @@ -395,7 +395,7 @@ struct task_struct *pick_next_task_idle(struct rq *rq) { struct task_struct *next = rq->idle; - set_next_task_idle(rq, next); + set_next_task_idle(rq, next, true); return next; } diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 38027c04b04c..e591d40fd645 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1515,13 +1515,16 @@ static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p, int flag #endif } -static inline void set_next_task_rt(struct rq *rq, struct task_struct *p) +static inline void set_next_task_rt(struct rq *rq, struct task_struct *p, bool first) { p->se.exec_start = rq_clock_task(rq); /* The running task is never eligible for pushing */ dequeue_pushable_task(rq, p); + if (!first) + return; + /* * If prev task was rt, put_prev_task() has already updated the * utilization. We only care of the case where we start to schedule a @@ -1572,7 +1575,7 @@ static struct task_struct *pick_next_task_rt(struct rq *rq) return NULL; p = _pick_next_task_rt(rq); - set_next_task_rt(rq, p); + set_next_task_rt(rq, p, true); return p; } diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 75d96cce1492..05c282775f21 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1716,7 +1716,7 @@ struct sched_class { struct task_struct *(*pick_next_task)(struct rq *rq); void (*put_prev_task)(struct rq *rq, struct task_struct *p); - void (*set_next_task)(struct rq *rq, struct task_struct *p); + void (*set_next_task)(struct rq *rq, struct task_struct *p, bool first); #ifdef CONFIG_SMP int (*balance)(struct rq *rq, struct task_struct *prev, struct rq_flags *rf); @@ -1768,7 +1768,7 @@ static inline void put_prev_task(struct rq *rq, struct task_struct *prev) static inline void set_next_task(struct rq *rq, struct task_struct *next) { WARN_ON_ONCE(rq->curr != next); - next->sched_class->set_next_task(rq, next); + next->sched_class->set_next_task(rq, next, false); } #ifdef CONFIG_SMP diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c index 0aefdfb79b36..4c9e9975684f 100644 --- a/kernel/sched/stop_task.c +++ b/kernel/sched/stop_task.c @@ -29,7 +29,7 @@ check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags) /* we're never preempted */ } -static void set_next_task_stop(struct rq *rq, struct task_struct *stop) +static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first) { stop->se.exec_start = rq_clock_task(rq); } @@ -39,7 +39,7 @@ static struct task_struct *pick_next_task_stop(struct rq *rq) if (!sched_stop_runnable(rq)) return NULL; - set_next_task_stop(rq, rq->stop); + set_next_task_stop(rq, rq->stop, true); return rq->stop; }