linux-kernel - Re: [PATCH 05/19] sched/numa: Use task faults only if numa

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Date:   Mon, 4 Jun 2018 06:09:34 -0700
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 05/19] sched/numa: Use task faults only if numa_group is
 not yet setup

> > Testcase       Time:         Min         Max         Avg      StdDev 	 %Change
> > numa01.sh      Real:      478.45      565.90      515.11       30.87 	 16.29%
> > numa01.sh       Sys:      207.79      271.04      232.94       21.33 	 -15.8%
> > numa01.sh      User:    39763.93    47303.12    43210.73     2644.86 	 14.04%
> > numa02.sh      Real:       60.00       61.46       60.78        0.49 	 0.871%
> > numa02.sh       Sys:       15.71       25.31       20.69        3.42 	 17.35%
> > numa02.sh      User:     5175.92     5265.86     5235.97       32.82 	 0.464%
> > numa03.sh      Real:      776.42      834.85      806.01       23.22 	 -7.47%
> > numa03.sh       Sys:      114.43      128.75      121.65        5.49 	 -19.5%
> > numa03.sh      User:    60773.93    64855.25    62616.91     1576.39 	 -5.36%
> > numa04.sh      Real:      456.93      511.95      482.91       20.88 	 2.930%
> > numa04.sh       Sys:      178.09      460.89      356.86       94.58 	 -11.3%
> > numa04.sh      User:    36312.09    42553.24    39623.21     2247.96 	 0.246%
> > numa05.sh      Real:      393.98      493.48      436.61       35.59 	 0.677%
> > numa05.sh       Sys:      164.49      329.15      265.87       61.78 	 38.92%
> > numa05.sh      User:    33182.65    36654.53    35074.51     1187.71 	 3.368%
> > 
> > Ideally this change shouldn't have affected performance.
> 
> Ideally you go on here to explain why it does in fact do affect
> performance.. :-)

I know it looks bad, but I have been unable to figure out why this patch
affects performance. I repeated the experiment multiple times to recheck
if it was not a one off problem. While there is a variance in different
runs, we do see a change in numbers before and after this patch atleast
on my machine.