linux-kernel - Re: [Priority Inheritance] SCHED_FIFO or SCHED

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Date:	Sat, 01 Oct 2011 07:41:09 +0200
From:	Mike Galbraith <efault@....de>
To:	"Tadeus (Eus) Prastowo" <0x657573@...glemail.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [Priority Inheritance] SCHED_FIFO or SCHED_RR?

On Fri, 2011-09-30 at 21:12 +0200, Tadeus (Eus) Prastowo wrote:
> Anyone familiar with the Linux scheduler, please?
> 
> On Wed, Sep 28, 2011 at 1:06 AM, Tadeus (Eus) Prastowo
> <0x657573@...glemail.com> wrote:
> > Hi!
> >
> > When a SCHED_RR task with RT priority X blocks on a
> > priority-inheriting mutex held by a SCHED_NORMAL task with nice value
> > Y, RT-Mutex code will change the SCHED_NORMAL task priority to that of
> > the SCHED_RR task and based on the new priority, will change the
> > scheduling class too. But, each task retains its own scheduling
> > policy.
> >
> > This means that the task inheriting the SCHED_RR priority will be
> > scheduled using SCHED_FIFO policy because task_tick_rt does not
> > enforce the SCHED_RR time slice when the task policy is not SCHED_RR.
> >
> > Why should a SCHED_NORMAL task inheriting the priority of a SCHED_RR
> > task get the privilege of SCHED_FIFO task for running as long as it
> > wishes even when the task giving the inheritance does not have such
> > privilege?

Existence of a critical section > slice would be the real problem, no?

	-Mike

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