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sched: Micro optimization in pick_next_task() and in check_preempt_curr()

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This introduces an optimization based on xxx_sched_class addresses
in two hot scheduler functions: pick_next_task() and check_preempt_curr().

It is possible to compare pointers to sched classes to check, which
of them has a higher priority, instead of current iterations using
for_each_class().

One more result of the patch is that size of object file becomes a little
less (excluding added BUG_ON(), which goes in __init section):

$size kernel/sched/core.o
         text     data      bss	    dec	    hex	filename
before:  66446    18957	    676	  86079	  1503f	kernel/sched/core.o
after:   66398    18957	    676	  86031	  1500f	kernel/sched/core.o

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/711a9c4b-ff32-1136-b848-17c622d548f3@yandex.ru
This commit is contained in:
Kirill Tkhai 2019-12-19 16:44:55 -05:00 committed by Peter Zijlstra
parent a87e749e8f
commit aa93cd53bc
1 changed files with 4 additions and 15 deletions
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19
kernel/sched/core.c
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@ -1412,20 +1412,10 @@ static inline void check_class_changed(struct rq *rq, struct task_struct *p,
void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
{
const struct sched_class *class;
if (p->sched_class == rq->curr->sched_class) {
if (p->sched_class == rq->curr->sched_class)
rq->curr->sched_class->check_preempt_curr(rq, p, flags);
} else {
for_each_class(class) {
if (class == rq->curr->sched_class)
break;
if (class == p->sched_class) {
resched_curr(rq);
break;
}
}
}
else if (p->sched_class > rq->curr->sched_class)
resched_curr(rq);
/*
* A queue event has occurred, and we're going to schedule. In
@ -4003,8 +3993,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
* higher scheduling class, because otherwise those loose the
* opportunity to pull in more work from other CPUs.
*/
if (likely((prev->sched_class == &idle_sched_class ||
prev->sched_class == &fair_sched_class) &&
if (likely(prev->sched_class <= &fair_sched_class &&
rq->nr_running == rq->cfs.h_nr_running)) {
p = pick_next_task_fair(rq, prev, rf);