linux-kernel - Re: [PATCH 4/4] sched/numa: Do not move imbalanced load purely on the basis of an idle CPU

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Date:   Wed, 12 Sep 2018 11:57:42 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] sched/numa: Do not move imbalanced load purely on
 the basis of an idle CPU


* Srikar Dronamraju <srikar@...ux.vnet.ibm.com> wrote:

> * Mel Gorman <mgorman@...hsingularity.net> [2018-09-10 10:41:47]:
> 
> > On Fri, Sep 07, 2018 at 01:37:39PM +0100, Mel Gorman wrote:
> > > > Srikar's patch here:
> > > > 
> > > >   http://lkml.kernel.org/r/1533276841-16341-4-git-send-email-srikar@linux.vnet.ibm.com
> > > > 
> > > > Also frobs this condition, but in a less radical way. Does that yield
> > > > similar results?
> > > 
> > > I can check. I do wonder of course if the less radical approach just means
> > > that automatic NUMA balancing and the load balancer simply disagree about
> > > placement at a different time. It'll take a few days to have an answer as
> > > the battery of workloads to check this take ages.
> > > 
> > 
> > Tests completed over the weekend and I've found that the performance of
> > both patches are very similar for two machines (both 2 socket) running a
> > variety of workloads. Hence, I'm not worried about which patch gets picked
> > up. However, I would prefer my own on the grounds that the additional
> > complexity does not appear to get us anything. Of course, that changes if
> > Srikar's tests on his larger ppc64 machines show the more complex approach
> > is justified.
> > 
> 
> Running SPECJbb2005. Higher bops are better.
> 
> Kernel A = 4.18+ 13 sched patches part of v4.19-rc1.
> Kernel B = Kernel A + 6 patches (http://lore.kernel.org/lkml/1533276841-16341-1-git-send-email-srikar@linux.vnet.ibm.com)
> Kernel C = Kernel B - (Avoid task migration for small numa improvement) i.e
> 	http://lore.kernel.org/lkml/1533276841-16341-4-git-send-email-srikar@linux.vnet.ibm.com
> 	+ 2 patches from Mel
> 	(Do not move imbalanced load purely)
> 	http://lore.kernel.org/lkml/20180907101139.20760-5-mgorman@techsingularity.net
> 	(Stop comparing tasks for NUMA placement)
> 	http://lore.kernel.org/lkml/20180907101139.20760-4-mgorman@techsingularity.net

We absolutely need the 'best' pre-regression baseline kernel measurements as well - was it 
vanilla v4.17?

Thanks,

	Ingo