* Siddha, Suresh B <[email protected]> wrote:
> On Tue, Aug 02, 2005 at 11:27:17AM +0200, Ingo Molnar wrote:
> >
> > * Siddha, Suresh B <[email protected]> wrote:
> >
> > > Jack Steiner brought this issue at my OLS talk.
> > >
> > > Take a scenario where two tasks are pinned to two HT threads in a physical
> > > package. Idle packages in the system will keep kicking migration_thread
> > > on the busy package with out any success.
> > >
> > > We will run into similar scenarios in the presence of CMP/NUMA.
> > >
> > > Patch appended.
> > >
> > > Signed-off-by: Suresh Siddha <[email protected]>
> >
> > nice catch!
> >
> > fine for -mm, but i dont think we need this fix in 2.6.13, as the effect
> > of the bug is an extra context-switch per 'CPU goes idle' event, in this
> > very specific (and arguably broken) task binding scenario.
>
> No. This is not a broken scenario. Its possible in NUMA case aswell.
>
> For example, lets take two nodes each having two physical packages.
> And assume that there are two tasks and both of them are on (may or
> may n't be pinned) two packages in node-0
>
> Todays load balance will detect that there is an imbalance between the
> two nodes and will try to distribute the load between the nodes.
>
> In general, we should allow the load of a group to grow upto its
> cpu_power and stop preventing these costly movements.
>
> Appended patch will fix this. I have done limited testing of this
> patch. Guys with big NUMA boxes, please give this patch a try.
makes sense in general - we should not try to move things around when we
are under-utilized. (In theory there could be heavily fluctuating
workloads which do not produce an above 100% average utilization, and
which could benefit from a perfectly even distribution of tasks - but i
dont think the load-balancer should care, as load-balancing is mostly a
"slow" mechanism.)
Again, 2.6.14 stuff.
Acked-by: Ingo Molnar <[email protected]>
Ingo
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