The following commit has been merged into the sched/core branch of tip:
Commit-ID: aa93cd53bc1b91b5f99c7b55e3dcc1ac98e99558
Gitweb:
https://git.kernel.org/tip/aa93cd53bc1b91b5f99c7b55e3dcc1ac98e99558
Author: Kirill Tkhai <[email protected]>
AuthorDate: Thu, 19 Dec 2019 16:44:55 -05:00
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Thu, 25 Jun 2020 13:45:44 +02:00
sched: Micro optimization in pick_next_task() and in check_preempt_curr()
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 <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
---
kernel/sched/core.c | 19 ++++---------------
1 file changed, 4 insertions(+), 15 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 81640fe..0a08d0c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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);
