Commit-ID: 49ee576809d837442624ac18804b07943267cd57
Gitweb: http://git.kernel.org/tip/49ee576809d837442624ac18804b07943267cd57
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 19 Jan 2017 18:44:08 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 30 Jan 2017 11:46:34 +0100
sched/core: Optimize pick_next_task() for idle_sched_class
Steve noticed that when we switch from IDLE to SCHED_OTHER we fail to
take the shortcut, even though all runnable tasks are of the fair
class, because prev->sched_class != &fair_sched_class.
Since I reworked the put_prev_task() stuff, we don't really care about
prev->class here, so removing that condition will allow this case.
This increases the likely case from 78% to 98% correct for Steve's
workload.
Reported-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Tested-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170119174408.GN6485@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/core.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 49ce1cb..51ca21e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3321,15 +3321,14 @@ static inline void schedule_debug(struct task_struct *prev)
static inline struct task_struct *
pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
- const struct sched_class *class = &fair_sched_class;
+ const struct sched_class *class;
struct task_struct *p;
/*
* Optimization: we know that if all tasks are in
* the fair class we can call that function directly:
*/
- if (likely(prev->sched_class == class &&
- rq->nr_running == rq->cfs.h_nr_running)) {
+ if (likely(rq->nr_running == rq->cfs.h_nr_running)) {
p = fair_sched_class.pick_next_task(rq, prev, rf);
if (unlikely(p == RETRY_TASK))
goto again;
--
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