linux-kernel - Re: [RFC PATCH 1 1/1] sched/numa: Hot VMA and shared VMA optimization

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Date: Tue, 25 Jun 2024 22:20:16 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: Raghavendra K T <raghavendra.kt@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, Ingo Molnar
	<mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Mel Gorman
	<mgorman@...e.de>, Andrew Morton <akpm@...ux-foundation.org>, "David
 Hildenbrand" <david@...hat.com>, <rppt@...nel.org>, Juri Lelli
	<juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>,
	Bharata B Rao <bharata@....com>, Johannes Weiner <jweiner@...com>, "kernel
 test robot" <oliver.sang@...el.com>, Yujie Liu <yujie.liu@...el.com>
Subject: Re: [RFC PATCH 1 1/1] sched/numa: Hot VMA and shared VMA optimization

Hi Raghavendra,

On 2024-03-22 at 19:11:12 +0530, Raghavendra K T wrote:
> Optimizations are based on history of PIDs accessing VMA.
> 
> - Increase tasks' access history windows (PeterZ) from 2 to 4.
> ( This patch is from Peter Zijlstra <peterz@...radead.org>)
> 
> Idea: A task is allowed to scan a VMA if:
> - VMA was very recently accessed as indicated by the latest
>   access PIDs information (hot VMA).
> - VMA is shared by more than 2 tasks. Here whole history of VMA's
> access PIDs is considered using bitmap_weight().
> 
> Signed-off-by: Raghavendra K T <raghavendra.kt@....com>
> ---
> I will split the patset and post if we find this pathset useful
> going further. First patch is from PeterZ.
> 

This is a good direction I think. We did an initial test using autonumabench
THREADLOCAL on a 240 CPUs 2 nodes system. It seems that this patch does not
show obvious difference, but it shows a more stable result(less run-to-run
variance). We'll enable the Sub-Numa-Cluster to see if there is any difference.
My understanding is that, if we can extend the NR_ACCESS_PID_HIST further,
the THREADLOCAL could see more benefits, as each thread has its own VMA. Or maybe
make the length of VMA access history adaptive(rather than a fixed 4) could be
more flexible.
                                          numa_scan_orig    numa_scan_4_history
Min       syst-NUMA01_THREADLOCAL      388.47 (   0.00%)      397.43 (  -2.31%)
Min       elsp-NUMA01_THREADLOCAL       40.27 (   0.00%)       38.94 (   3.30%)
Amean     syst-NUMA01_THREADLOCAL      467.62 (   0.00%)      459.10 (   1.82%)
Amean     elsp-NUMA01_THREADLOCAL       42.20 (   0.00%)       44.84 (  -6.26%)
Stddev    syst-NUMA01_THREADLOCAL       74.11 (   0.00%)       60.90 (  17.81%)
CoeffVar  syst-NUMA01_THREADLOCAL       15.85 (   0.00%)       13.27 (  16.29%)
Max       syst-NUMA01_THREADLOCAL      535.36 (   0.00%)      519.21 (   3.02%)
Max       elsp-NUMA01_THREADLOCAL       43.96 (   0.00%)       56.33 ( -28.14%)
BAmean-50 syst-NUMA01_THREADLOCAL      388.47 (   0.00%)      397.43 (  -2.31%)
BAmean-50 elsp-NUMA01_THREADLOCAL       40.27 (   0.00%)       38.94 (   3.30%)
BAmean-95 syst-NUMA01_THREADLOCAL      433.75 (   0.00%)      429.05 (   1.08%)
BAmean-95 elsp-NUMA01_THREADLOCAL       41.31 (   0.00%)       39.09 (   5.39%)
BAmean-99 syst-NUMA01_THREADLOCAL      433.75 (   0.00%)      429.05 (   1.08%)
BAmean-99 elsp-NUMA01_THREADLOCAL       41.31 (   0.00%)       39.09 (   5.39%)

thanks,
Chenyu