Subject: Scheduler RR, first time slice wrong?
From: Andreas Huber <andreas.huber@keymile.com>
To: linux-kernel@vger.kernel.org
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Date: Thu, 06 Nov 2008 08:22:47 +0100
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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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