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

Feng Tang
2021-05-31T12:00:27Z

On Fri, May 28, 2021 at 09:17:41AM -0700, Dave Hansen wrote:
> On 5/28/21 8:18 AM, Mel Gorman wrote:
> >> 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.
>
> It's a Cascade Lake as well. But, I never trust hardware at a hardware
> company. These could be preproduction CPUs or BIOS or both, or have
> some bonkers configuration knob flipped.
>
> It's also got a bunch of PMEM plugged and onlined, including the
> _possibility_ of kernel data structures ended up on PMEM. They *mostly*
> don't end up there, but it does happen on occasion.
>
> Anyway, I'll see if we can do some more runs with your latest version.
> It looks like it's been picked up for -mm so 0day should be pounding on
> it soon enough.

Yes, usually 0day has more benchmark test covering -mm tree.

As for the kbuild test run for v2, after more runs, the previous 2%
longer kbuild time turns to 1% shorter time, seems to be in normal
deviation range.

Also I checked Mel's v3 branch which has the fix for cpuless node,
the pcp 'high' looks normal on PMEM node:

pagesets
cpu: 0
count: 67
high: 724
batch: 63
vm stats threshold: 125

Thanks,
Feng