Date: Thu, 6 Nov 2008 08:44:50 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Andreas Huber <andreas.huber@keymile.com>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Mike Galbraith <efault@gmx.de>,
       Dmitry Adamushko <dmitry.adamushko@gmail.com>
Subject: Re: Scheduler RR, first time slice wrong?
Message-ID: <20081106074449.GC8459@elte.hu>
References: <1225956167.4472.27.camel@chber1-10446x.ch.keymile.net>
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(added Cc:s)

* Andreas Huber <andreas.huber@keymile.com> wrote:

> Hi,
> 
> when starting a real-time process with the round-robin scheduler, the
> first time slice is set to HZ (1 second).
> When starting two such processes at the same time of the same static
> priority, the second one started is first executed after 1 second.
> (supposing the first process is heavy on cpu load).
> After both have exhausted this first time slice, it is set to
> DEF_TIMESLICE (which is 100ms).
> 
> Is this behavior as it is supposed to be?
> 
> Please add me in CC.
> 
> Regards,
> Andreas
> 
> 
> Relevant parts in the code:
> include/linux/init_task.h
> #define INIT_TASK(tsk) \
> 	.rt	= { \
> 		.time_slice = HZ,
> 
> kernel/sched.c
> #define DEF_TIMESLICE   (100 * HZ / 1000)
> 
> kernel/sched_rt.c
> static void task_tick_rt(struct rq *rq, struct task_struct *p, int
> queued)
>   if (--p->rt.time_slice)
>     return;
> 
>   p->rt.time_slice = DEF_TIMESLICE;
> 
> --
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