lkml.org 
[lkml]   [2021]   [Dec]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/2] sched/fair: Use weight of SD_NUMA domain in find_busiest_group
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

\
 
 \ /
  Last update: 2021-12-21 12:33    [W:0.058 / U:0.564 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site