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

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Date:   Mon, 31 May 2021 20:00:15 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hillf Danton <hdanton@...a.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 0/6 v2] Calculate pcp->high based on zone sizes and
 active CPUs

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