Messages in this thread Patch in this message | | | Subject | Re: allow the load to grow upto its cpu_power (was Re: [Patch] don't kick ALB in the presence of pinned task) | From | Nick Piggin <> | Date | Thu, 11 Aug 2005 13:09:10 +1000 |
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On Tue, 2005-08-09 at 19:03 -0700, Siddha, Suresh B wrote: > On Wed, Aug 10, 2005 at 10:27:44AM +1000, Nick Piggin wrote: > > Yeah this makes sense. Thanks. > > > > I think we'll only need your first line change to fix this, though. > > > > Your second change will break situations where a single group is very > > loaded, but it is in a domain with lots of cpu_power > > (total_load <= total_power). > > In that case, we will move the excess load from that group to some > other group which is below its capacity. Instead of bringing everyone > to avg load, we make sure that everyone is at or below its cpu_power. > This will minimize the movements between the nodes. > > For example, Let us assume sched groups node-0, node-1 each has > 4*SCHED_LOAD_SCALE as its cpu_power. > > And with 6 tasks on node-0 and 0 on node-1, current load balance > will move 3 tasks from node-0 to 1. But with my patch, it will move only > 2 tasks to node-1. Is this what you are referring to as breakage? >
No, I had thought it was possible to get into a situation where one queue could be very loaded but not have anyone to pull from it if total_load <= total_pwr.
I see that shouldn't happen though.
I have a variation on the 2nd part of your patch which I think I would prefer. IMO it kind of generalises the current imbalance calculation to handle this case rather than introducing a new special case.
Untested as yet, but I'll queue it to send to Andrew after it gets some testing - unless you have any objections that is.
Thanks, Nick
-- SUSE Labs, Novell Inc.
Don't pull tasks from a group if that would cause the group's total load to drop below its total cpu_power (ie. cause the group to start going idle).
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> Signed-off-by: Nick Piggin <npiggin@suse.de>
Index: linux-2.6/kernel/sched.c =================================================================== --- linux-2.6.orig/kernel/sched.c 2005-08-11 12:10:10.199651212 +1000 +++ linux-2.6/kernel/sched.c 2005-08-11 12:53:15.361971195 +1000 @@ -1886,6 +1886,7 @@ { struct sched_group *busiest = NULL, *this = NULL, *group = sd->groups; unsigned long max_load, avg_load, total_load, this_load, total_pwr; + unsigned long max_pull; int load_idx; max_load = this_load = total_load = total_pwr = 0; @@ -1932,7 +1933,7 @@ group = group->next; } while (group != sd->groups); - if (!busiest || this_load >= max_load) + if (!busiest || this_load >= max_load || max_load <= SCHED_LOAD_SCALE) goto out_balanced; avg_load = (SCHED_LOAD_SCALE * total_load) / total_pwr; @@ -1952,8 +1953,12 @@ * by pulling tasks to us. Be careful of negative numbers as they'll * appear as very large values with unsigned longs. */ + + /* Don't want to pull so many tasks that a group would go idle */ + max_pull = min(max_load - avg_load, max_load - SCHED_LOAD_SCALE); + /* How much load to actually move to equalise the imbalance */ - *imbalance = min((max_load - avg_load) * busiest->cpu_power, + *imbalance = min(max_pull * busiest->cpu_power, (avg_load - this_load) * this->cpu_power) / SCHED_LOAD_SCALE; | |