Re: [PATCH 0/6 v2] Calculate pcp->high based on zone sizes and active CPUs

Mel Gorman
2021-05-28T15:18:52Z

On Fri, May 28, 2021 at 07:39:29AM -0700, Dave Hansen wrote:
> On 5/28/21 1:55 AM, Mel Gorman wrote:
> > - * onlined.
> > - */
> > - nr_local_cpus = max(1U, cpumask_weight(cpumask_of_node(zone_to_nid(zone)))) + cpu_online;
> > - high = total_pages / nr_local_cpus;
> > + * onlined. For memory nodes that have no CPUs, split pcp->high across
> > + * all online CPUs to mitigate the risk that reclaim is triggered
> > + * prematurely due to pages stored on pcp lists.
> > + */
> > + nr_split_cpus = cpumask_weight(cpumask_of_node(zone_to_nid(zone))) + cpu_online;
> > + if (!nr_split_cpus)
> > + nr_split_cpus = num_online_cpus();
> > + high = total_pages / nr_split_cpus;
>
> Updated version looks fine to me, thanks!
>
> BTW, to do some of this testing, Feng was doing a plain old kernel
> build. On the one system where this got run, he noted a ~2% regression
> in build times. Nothing major, but you might want to be on the lookout
> in case 0day or the other test harnesses find something similar once
> this series gets to them.
>

What type of system was it?

I noticed minor differences for some thread counts on kernel compilations
but for CascadeLake at least, it was mostly neutral. Below is an old test
result based on a previous revision.

kernbench
5.13.0-rc2 5.13.0-rc2
vanilla mm-pcpburst-v2r3
Amean elsp-2 469.22 ( 0.00%) 470.03 * -0.17%*
Amean elsp-4 251.03 ( 0.00%) 250.83 ( 0.08%)
Amean elsp-8 131.39 ( 0.00%) 130.89 ( 0.38%)
Amean elsp-16 74.37 ( 0.00%) 75.11 ( -0.99%)
Amean elsp-32 42.10 ( 0.00%) 42.20 ( -0.24%)
Amean elsp-64 32.21 ( 0.00%) 32.14 ( 0.23%)
Amean elsp-128 31.59 ( 0.00%) 31.68 ( -0.27%)
Amean elsp-160 31.76 ( 0.00%) 31.69 ( 0.21%)

A Haswell machine showed the worst results for kernbench

Amean elsp-2 459.99 ( 0.00%) 465.27 * -1.15%*
Amean elsp-4 250.76 ( 0.00%) 253.17 * -0.96%*
Amean elsp-8 141.28 ( 0.00%) 141.78 ( -0.36%)
Amean elsp-16 77.71 ( 0.00%) 77.88 ( -0.22%)
Amean elsp-32 44.09 ( 0.00%) 44.40 ( -0.69%)
Amean elsp-64 33.79 ( 0.00%) 33.46 ( 0.96%)
Amean elsp-128 33.14 ( 0.00%) 33.26 ( -0.37%)
Amean elsp-160 33.26 ( 0.00%) 33.36 * -0.30%*

The series with review feedback and dealing with cpuless nodes is queued
and should complete over the weekend.

> Acked-by: Dave Hansen <dave.hansen@intel.com>

Thanks!

--
Mel Gorman
SUSE Labs