Messages in this thread | | | Date | Fri, 07 Jul 2023 09:44:55 +0200 | From | Tobias Huschle <> | Subject | Re: [RFC 1/1] sched/fair: Consider asymmetric scheduler groups in load balancer |
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On 2023-07-04 15:40, Peter Zijlstra wrote: > On Mon, May 15, 2023 at 01:46:01PM +0200, Tobias Huschle wrote: >> The current load balancer implementation implies that scheduler >> groups, >> within the same domain, all host the same number of CPUs. This is >> reflected in the condition, that a scheduler group, which is load >> balancing and classified as having spare capacity, should pull work >> from the busiest group, if the local group runs less processes than >> the busiest one. This implies that these two groups should run the >> same number of processes, which is problematic if the groups are not >> of the same size. >> >> The assumption that scheduler groups within the same scheduler domain >> host the same number of CPUs appears to be true for non-s390 >> architectures. > > Mostly; there's historically the cpuset case where we can create > lopsided groups like that. And today we're growing all these hybrid > things that will also tickle this, except they're looking towards > different balancer extentions to deal with the IPC difference so might > not be immediately caring about this here issue. > > >> Signed-off-by: Tobias Huschle <huschle@linux.ibm.com> >> --- >> kernel/sched/fair.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 48b6f0ca13ac..b1307d7e4065 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -10426,7 +10426,8 @@ static struct sched_group >> *find_busiest_group(struct lb_env *env) >> * group's child domain. >> */ >> if (sds.prefer_sibling && local->group_type == group_has_spare && >> - busiest->sum_nr_running > local->sum_nr_running + 1) >> + busiest->sum_nr_running * local->group_weight > >> + local->sum_nr_running * busiest->group_weight + 1) > > Should that not be: busiest->group_weight * (local->sum_nr_running + 1) > ?
I agree, adding the brackets makes more sense and is clearer on what's intended by this check while also preserving the original behavior for local->group_weight == busiest->group_weight
> > I'm not opposed to this -- it seems fairly straight forward.
Appreciated, I will go ahead and send a patch once I incorporated the other feedback I got. Thanks.
> >> goto force_balance; >> >> if (busiest->group_type != group_overloaded) { >> -- >> 2.34.1 >>
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