Re: [PATCH] sched/numa: use runnable_avg to classify node

[Mel Gorman]

On Tue, Aug 25, 2020 at 02:18:18PM +0200, Vincent Guittot wrote:
> Use runnable_avg to classify numa node state similarly to what is done for
> normal load balancer. This helps to ensure that numa and normal balancers
> use the same view of the state of the system.
> 
> - large arm64system: 2 nodes / 224 CPUs
> hackbench -l (256000/#grp) -g #grp
> 
> grp    tip/sched/core         +patchset              improvement
> 1      14,008(+/- 4,99 %)     13,800(+/- 3.88 %)     1,48 %
> 4       4,340(+/- 5.35 %)      4.283(+/- 4.85 %)     1,33 %
> 16      3,357(+/- 0.55 %)      3.359(+/- 0.54 %)    -0,06 %
> 32      3,050(+/- 0.94 %)      3.039(+/- 1,06 %)     0,38 %
> 64      2.968(+/- 1,85 %)      3.006(+/- 2.92 %)    -1.27 %
> 128     3,290(+/-12.61 %)      3,108(+/- 5.97 %)     5.51 %
> 256     3.235(+/- 3.95 %)      3,188(+/- 2.83 %)     1.45 %
> 

Intuitively the patch makes sense but I'm not a fan of using hackbench
for evaluating NUMA balancing. The tasks are too short-lived and it's
not sensitive enough to data placement because of the small footprint
and because hackbench tends to saturate a machine.

As predicting NUMA balancing behaviour in your head can be difficult, I've
queued up a battery of tests on a few different NUMA machines and will see
what falls out. It'll take a few days as some of the tests are long-lived.

Baseline will be 5.9-rc2 as I haven't looked at the topology rework in
tip/sched/core and this patch should not be related to it.

-- 
Mel Gorman
SUSE Labs