Re: [ckrm-tech] Re: [PATCH 0/9] CPU controller

[Mike Galbraith <efault@gmx.de>]

On Fri, 2006-04-28 at 12:13 +0400, Kirill Korotaev wrote:
> >>>I'm also pretty sure, that CPU controller based on timeslice tricks 
> >>>behaves poorly on burstable load patterns as well and with interactive 
> >>>tasks. So before commiting I propose to perform a good testing on 
> >>>different load patterns.
> >>
> >>Yes, it can only react very slowly.
> > 
> > 
> > Actually, this might not be that much of a problem.  I know I can
> > traverse queue heads periodically very cheaply.  Traversing both active
> > and expired arrays to requeue starving tasks once every 100ms costs max
> > 4usecs (3GHz P4) for a typical distribution.
> 
> with fair scheduling with can be a big problem, as tasks working less 
> then a tick are hard to account :/

Yeah, tasks dodging the timer interrupt can steal considerable time.  I
instrumented this once, and caught tasks stealing in excess of 30% of
the timeslice of their more lethargic brothers.  Generally, they get
caught often enough that statistics ~evens the playing field.

	-Mike