Messages in this thread | | | Date | Tue, 21 Dec 2021 11:32:27 +0000 | From | Mel Gorman <> | Subject | Re: [PATCH 1/2] sched/fair: Use weight of SD_NUMA domain in find_busiest_group |
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On Tue, Dec 21, 2021 at 11:53:50AM +0100, Vincent Guittot wrote: > On Fri, 10 Dec 2021 at 10:33, Mel Gorman <mgorman@techsingularity.net> wrote: > > > > find_busiest_group uses the child domain's group weight instead of > > the sched_domain's weight that has SD_NUMA set when calculating the > > allowed imbalance between NUMA nodes. This is wrong and inconsistent > > with find_idlest_group. > > I agree that find_busiest_group and find_idlest_group should be > consistent and use the same parameters but I wonder if sched_domain's > weight is the right one to use instead of the target group's weight. >
Ok
> IIRC, the goal of adjust_numa_imbalance is to keep some threads on the > same node as long as we consider that there is no performance impact > because of sharing resources as they can even take advantage of > locality if they interact.
Yes.
> So we consider that tasks will not be > impacted by sharing resources if they use less than 25% of the CPUs of > a node. If we use the sd->span_weight instead, we consider that we can > pack threads in the same node as long as it uses less than 25% of the > CPUs in all nodes. >
I assume you mean the target group weight instead of the node. The primary resource we are concerned with is memory bandwidth and it's a guess because we do not know for sure where memory channels are or how they are configured in this context and it may or may not be correlated with groups. I think using the group instead would deserve a series on its own after settling on an imbalance number when there are multiple LLCs per node.
-- Mel Gorman SUSE Labs
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