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

[Peter Williams]

William Lee Irwin III wrote:
> * Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > Yes, there are potential compatibility problems.  Example: a machine 
> > > with 100 busy httpd processes and suddenly a big gzip starts up from 
> > > console or cron.
> [...]
>
> On Thu, Apr 19, 2007 at 08:38:10AM +0200, Ingo Molnar wrote:
> > hmmmm. How about the following then: default to nice -10 for all 
> > (SCHED_NORMAL) kernel threads and all root-owned tasks. Root _is_ 
> > special: root already has disk space reserved to it, root has special 
> > memory allocation allowances, etc. I dont see a reason why we couldnt by 
> > default make all root tasks have nice -10. This would be instantly loved 
> > by sysadmins i suspect ;-)
> > (distros that go the extra mile of making Xorg run under non-root could 
> > also go another extra one foot to renice that X server to -10.)
>
> 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.
>
> I believe root's default priority can be adjusted in userspace as
> things now stand somewhere in /etc/ but I'm not sure of the specifics.
> Word is somewhere in /etc/security/limits.conf

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).

Peter
--
Peter Williams                                   pwil3058@xxxxxxxxxxxxxx

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