linux-kernel - Re: [PATCH 4/4] sched/numa: Adjust imb_numa_nr to a better approximation of memory channels

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Message-ID: <20220519092913.GU3441@techsingularity.net>
Date:   Thu, 19 May 2022 10:29:13 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] sched/numa: Adjust imb_numa_nr to a better
 approximation of memory channels

On Wed, May 18, 2022 at 06:06:25PM +0100, Mel Gorman wrote:
> I'm running the tests to recheck exactly how much impact this patch has
> on the peak performance. It takes a few hours so I won't have anything
> until tomorrow.
> 

It wasn't my imagination, the last path was worth a few percent

v5.3                                     Min  95.84 Max  96.55 Range   0.71 Mean  96.16
v5.7                                     Min  95.44 Max  96.51 Range   1.07 Mean  96.14
v5.8                                     Min  96.02 Max 197.08 Range 101.06 Mean 154.70
v5.12                                    Min 104.45 Max 111.03 Range   6.58 Mean 105.94
v5.13                                    Min 104.38 Max 170.37 Range  65.99 Mean 117.35
v5.13-revert-c6f886546cb8                Min 104.40 Max 110.70 Range   6.30 Mean 105.68
v5.18rc4-baseline                        Min 110.78 Max 169.84 Range  59.06 Mean 131.22
v5.18rc4-revert-c6f886546cb8             Min 113.98 Max 117.29 Range   3.31 Mean 114.71
v5.18rc4-shiftimb3-v2r2                  Min  95.34 Max 165.75 Range  70.41 Mean 120.92
v5.18rc4-consistimb-v2r2                 Min 104.02 Max 175.22 Range  71.20 Mean 116.62
v5.18rc4-consistimb-revert-c6f886546cb8  Min 104.02 Max 112.56 Range   8.54 Mean 105.52

v5.18rc4-shiftimb3-v2r2  is patches 1-4
v5.18rc4-consistimb-v2r2 is patches 1-3

The last path is worth around 8% and is what's necessary to bring best
performance back to kernel v5.7 levels. As you can see from the range,
the result is unstable but reverting c6f886546cb8 reduces it by a lot.
Not enough to be at v5.7 levels but enough to indicate that the allowed
NUMA balance changes are not the sole source of the problem.

-- 
Mel Gorman
SUSE Labs