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

William Lee Irwin III
2007-04-19T07:58:19Z

* Andrew Morton <akpm@linux-foundation.org> 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

-- wli