linux-kernel - Re: [PATCH 2/2] sched: allow users with rtprio rlimit to change from SCHED

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Message-ID: <1298459826.2217.363.camel@twins>
Date:	Wed, 23 Feb 2011 12:17:06 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Darren Hart <dvhart@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	richard.purdie@...uxfoundation.org
Subject: Re: [PATCH 2/2] sched: allow users with rtprio rlimit to change
 from SCHED_IDLE policy

On Wed, 2011-02-23 at 12:13 +0100, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Tue, 2011-02-22 at 13:04 -0800, Darren Hart wrote:
> > > As it stands, users with rtprio rlimit permissions can change their policy from
> > > SCHED_OTHER to SCHED_FIFO and back. They can change to SCHED_IDLE, but not back
> > > to SCHED_FIFO. If they have the rtprio permission, they should be able to. Once
> > > in SCHED_FIFO, they could go back to SCHED_OTHER. This patch allows users with
> > > rtprio permission to change out of SCHED_IDLE.
> > > 
> > 
> > Ingo, can you remember the rationale for this?
> > 
> > The fact is that SCHED_IDLE is very near nice-20, and we can do:
> > 
> > peterz@...ns:~$ renice 5 -p $$
> > 1867: old priority 0, new priority 5
> > peterz@...ns:~$ renice 0 -p $$
> > 1867: old priority 5, new priority 0
> > 
> > Which would suggest that we should be able to return to SCHED_OTHER
> > RLIMIT_NICE-20.
> 
> I dont remember anything subtle there - most likely we just forgot about that spot 
> when adding RLIMIT_RTPRIO support.

Ah, I was arguing we should allow it regardless of RLIMIT_RTPRIO, based
on RLIMIT_NICE, it is after all a change to SCHED_OTHER, not
SCHED_FIFO/RR.


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