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

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Date:	Wed, 8 Aug 2007 14:34:18 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mitchell Erblich <erblichs@...thlink.net>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Question: RT schedular : task_tick_rt(struct rq *rq, struct
	task_struct *p) : decreases overhead when  rq->nr_running == 1

* Mitchell Erblich <erblichs@...thlink.net> wrote:

> 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...

your change is a possible optimization, but this is a pretty rare 
codepath because the overwhelming majority of RT apps uses SCHED_FIFO. 
Plus, the time_slice going down to 0 is a relatively rare event even for 
SCHED_RR tasks. And if we have only a single SCHED_RR task, why is it 
SCHED_RR to begin with? So this is on several levels an uncommon 
workload and by adding a check like that we'd increase the codesize. But 
... no strong feelings against this optimization - if you send a proper 
patch we can apply it, it certainly makes sense from a logic POV.

	Ingo
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