linux-kernel - Question: RT schedular : task_tick_rt(struct rq *rq, struct task_struct *p) : decreases overhead when rq->nr

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Date:	Tue, 7 Aug 2007 15:54:41 -0700
From:	"Mitchell Erblich" <erblichs@...thlink.net>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Question: RT schedular : task_tick_rt(struct rq *rq, struct task_struct *p) : decreases overhead when  rq->nr_running == 1

Ingo Molnar and group,

If their is a single RT task on this rq, then why not just reset the
timeslice and return??? Just MAYBE decreasing re-scheduling
overhead..

Thus,,,,

After
    p->time_slice = static_prio_timeslice(p->static_prio);

Why isn't their a check like
    if  (rq->nr_running == 1)
         return;

Which world remove the need for any recheduling
or requeue'ing...

Mitchell Erblich
FYI: below is believed to be a snap of the current/ orig func
-----------------------------


+static void task_tick_rt(struct rq *rq, struct task_struct *p)
+{
+ /*
+  * RR tasks need a special form of timeslice management.
+  * FIFO tasks have no timeslices.
+  */
+ if (p->policy != SCHED_RR)
+  return;
+
+ if (--p->time_slice)
+  return;
+
+ p->time_slice = static_prio_timeslice(p->static_prio);
+ set_tsk_need_resched(p);
+
+ /* put it at the end of the queue: */
+ requeue_task_rt(rq, p);
+}
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