Re: [PATCH 2/2] sched: allow users with rtprio rlimit to change fromSCHED_IDLE policy

[Darren Hart]

On 02/23/2011 03:17 AM, Peter Zijlstra wrote:
> On Wed, 2011-02-23 at 12:13 +0100, Ingo Molnar wrote:
> > * Peter Zijlstra<peterz@xxxxxxxxxxxxx>  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@twins:~$ renice 5 -p $$
> > > 1867: old priority 0, new priority 5
> > > peterz@twins:~$ renice 0 -p $$
> > > 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.

So we need an OR test of RLIMIT_NICE | RLIMIT_RTPRIO ? The reason I keep 
coming back to RTPRIO is it allows the user to change to 
SCHED_(FIFO|RR), and from there they can change to anything they want - 
so why force two steps? Perhaps the argument is to keep the meaning of 
the RLIMITs precise, and if you want to go from IDLE->OTHER you had 
better properly set RLIMIT_NICE - maybe I just convinced myself.

Shall I respin the patch to reflect that?


--
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel
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