linux-kernel - Re: [PATCH -mm] autonuma: Fix scan period updating

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Date:   Fri, 12 Jul 2019 13:50:47 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     huang ying <huang.ying.caritas@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, jhladky@...hat.com,
        lvenanci@...hat.com, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH -mm] autonuma: Fix scan period updating

On Fri, Jul 12, 2019 at 06:48:05PM +0800, Huang, Ying wrote:
> > Ordinarily I would hope that the patch was motivated by observed
> > behaviour so you have a metric for goodness. However, for NUMA balancing
> > I would typically run basic workloads first -- dbench, tbench, netperf,
> > hackbench and pipetest. The objective would be to measure the degree
> > automatic NUMA balancing is interfering with a basic workload to see if
> > they patch reduces the number of minor faults incurred even though there
> > is no NUMA balancing to be worried about. This measures the general
> > overhead of a patch. If your reasoning is correct, you'd expect lower
> > overhead.
> >
> > For balancing itself, I usually look at Andrea's original autonuma
> > benchmark, NAS Parallel Benchmark (D class usually although C class for
> > much older or smaller machines) and spec JBB 2005 and 2015. Of the JBB
> > benchmarks, 2005 is usually more reasonable for evaluating NUMA balancing
> > than 2015 is (which can be unstable for a variety of reasons). In this
> > case, I would be looking at whether the overhead is reduced, whether the
> > ratio of local hits is the same or improved and the primary metric of
> > each (time to completion for Andrea's and NAS, throughput for JBB).
> >
> > Even if there is no change to locality and the primary metric but there
> > is less scanning and overhead overall, it would still be an improvement.
> 
> Thanks a lot for your detailed guidance.
> 

No problem.

> > If you have trouble doing such an evaluation, I'll queue tests if they
> > are based on a patch that addresses the specific point of concern (scan
> > period not updated) as it's still not obvious why flipping the logic of
> > whether shared or private is considered was necessary.
> 
> I can do the evaluation, but it will take quite some time for me to
> setup and run all these benchmarks.  So if these benchmarks have already
> been setup in your environment, so that your extra effort is minimal, it
> will be great if you can queue tests for the patch.  Feel free to reject
> me for any inconvenience.
> 

They're not setup as such, but my testing infrastructure is heavily
automated so it's easy to do and I think it's worth looking at. If you
update your patch to target just the scan period aspects, I'll queue it
up and get back to you. It usually takes a few days for the automation
to finish whatever it's doing and pick up a patch for evaluation.

-- 
Mel Gorman
SUSE Labs