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

Ingo Molnar
2007-04-19T06:38:40Z

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

> > And yes, by fairly, I mean fairly among all threads as a base
> > resource class, because that's what Linux has always done
>
> 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.
>
> Under current kernels, that gzip will take ages and the httpds will
> take a 1% slowdown, which may well be exactly the behaviour which is
> desired.
>
> If we were to schedule by UID then the gzip suddenly gets 50% of the
> CPU and those httpd's all take a 50% hit, which could be quite
> serious.
>
> That's simple to fix via nicing, but people have to know to do that,
> and there will be a transition period where some disruption is
> possible.

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.)

Ingo