Re: [Announce] [patch] Modular Scheduler Core and Completely FairScheduler [CFS]

[Peter Williams]

William Lee Irwin III wrote:
> William Lee Irwin III wrote:
> > > I'd further recommend making priority levels accessible to kernel threads
> > > that are not otherwise accessible to processes, both above and below
> > > user-available priority levels. Basically, if you can get SCHED_RR and
> > > SCHED_FIFO to coexist as "intimate scheduler classes," then a SCHED_KERN
> > > scheduler class can coexist with SCHED_OTHER in like fashion, but with
> > > availability of higher and lower priorities than any userspace process
> > > is allowed, and potentially some differing scheduling semantics. In such
> > > a manner nonessential background processing intended not to ever disturb
> > > userspace can be given priorities appropriate to it (perhaps even con's
> > > SCHED_IDLEPRIO would make sense), and other, urgent processing can be
> > > given priority over userspace altogether.
>
> On Thu, Apr 19, 2007 at 09:50:19PM +1000, Peter Williams wrote:
> > This is sounding very much like System V Release 4 (and descendants) 
> > except that they call it SCHED_SYS and also give SCHED_NORMAL tasks that 
> > are in system mode dynamic priorities in the SCHED_SYS range (to avoid 
> > priority inversion, I believe).
>
> Descriptions of that are probably where I got the idea (hurrah for OS
> textbooks).

And long term background memory.  :-)

> It makes a fair amount of sense.

Yes.  You could also add a SCHED_IA in between SCHED_SYS and SCHED_OTHER 
(a la Solaris) for interactive tasks.  The only problem is how to get a 
task into SCHED_IA without root privileges.

> Not sure what the take on
> the specific precedent is. The only content here is expanding the
> priority range with ranges above and below for the exclusive use of
> ultra-privileged tasks, so it's really trivial. Actually it might be so
> trivial it should just be some permission checks in the SCHED_OTHER
> renicing code.

Perhaps.

Peter
--
Peter Williams                                   pwil3058@xxxxxxxxxxxxxx

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce
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