From: Peter Zijlstra peterz@infradead.org
commit a0e813f26ebcb25c0b5e504498fbd796cca1a4ba upstream.
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) 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 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 mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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(-)
--- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1743,13 +1743,16 @@ static void start_hrtick_dl(struct rq *r } #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);
@@ -1785,7 +1788,7 @@ pick_next_task_dl(struct rq *rq, struct 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; }
--- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10151,7 +10151,7 @@ static void switched_to_fair(struct rq * * 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;
--- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -385,7 +385,7 @@ static void put_prev_task_idle(struct rq { }
-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); @@ -399,7 +399,7 @@ pick_next_task_idle(struct rq *rq, struc if (prev) put_prev_task(rq, prev);
- set_next_task_idle(rq, next); + set_next_task_idle(rq, next, true);
return next; } --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1515,13 +1515,16 @@ static void check_preempt_curr_rt(struct #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 @@ -1575,7 +1578,7 @@ pick_next_task_rt(struct rq *rq, struct return NULL;
p = _pick_next_task_rt(rq); - set_next_task_rt(rq, p); + set_next_task_rt(rq, p, true); return p; }
--- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1728,7 +1728,7 @@ struct sched_class { struct task_struct *prev, struct rq_flags *rf); 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); @@ -1780,7 +1780,7 @@ static inline void put_prev_task(struct 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 --- a/kernel/sched/stop_task.c +++ b/kernel/sched/stop_task.c @@ -29,7 +29,7 @@ check_preempt_curr_stop(struct rq *rq, s /* 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); } @@ -42,7 +42,7 @@ pick_next_task_stop(struct rq *rq, struc 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; }