Messages in this thread | | | Date | Wed, 10 Aug 2005 09:16:08 +0200 | From | Ingo Molnar <> | Subject | Re: allow the load to grow upto its cpu_power (was Re: [Patch] don't kick ALB in the presence of pinned task) |
| |
* Siddha, Suresh B <suresh.b.siddha@intel.com> wrote:
> On Tue, Aug 02, 2005 at 11:27:17AM +0200, Ingo Molnar wrote: > > > > * Siddha, Suresh B <suresh.b.siddha@intel.com> 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 <suresh.b.siddha@intel.com> > > > > 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 <mingo@elte.hu>
Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |