Re: [PATCH 5/5] Only call rebalance_domains when needed from scheduler_tick

Christoph Lameter
2006-10-26T18:14:37Z

On Fri, 27 Oct 2006, Nick Piggin wrote:

> > > sched-domains was supposed to be able to build a whacky topology
> > > so you didn't have to take the occasional big latency hit when
> > > scanning 512 CPUs...
> >
> >
> > How is that supposed to work? The load calculations will be off
> > in that case and also the load balancing algorithm wont work anymore. This
> > is going to be a pretty significant rework of how the scheduler works but
> > given the problems with pinned tasks... maybe that is necessary?
> > duler?
>
> What will the problem be? Sure it may pull tasks fom one group to
> another when both could actually be pulling from a third, but it
> the load balancing algorithm should work fine and not require any
> rework.

Hmmm....
I think we already have what you want if we would disable the allnodes
domain. The next sched domain layer contains 16 surrounding nodes
from which it can pull processes. If there would be severe overload on one
node then processes would be gradually migrated away from it but it would
require multiple migration steps.

Nevertheless, I still think we need this patchset because of the general
interrupt hold off issue. The livelock is extreme case but it general we
do no want long interrupt holdoffs but keep the period in which we would
be executing with interrupts off minimal.