linux-kernel - Re: [PATCH] mm/vmstat: Defer the refresh_zone_stat

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Message-Id: <20240810000404.b08cb06ebbba7e0de9bb8c72@linux-foundation.org>
Date: Sat, 10 Aug 2024 00:04:04 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, ssengar@...rosoft.com,
 wei.liu@...nel.org
Subject: Re: [PATCH] mm/vmstat: Defer the refresh_zone_stat_thresholds after
 all CPUs bringup

On Mon, 8 Jul 2024 21:57:50 -0700 Saurabh Singh Sengar <ssengar@...ux.microsoft.com> wrote:

> > > No NUMA = 1024*2*1*512  =   1,048,576 : Here refresh_zone_stat_thresholds
> > > takes around 224 ms total for all the CPUs in the system under test.
> > > 16 NUMA = 1024*2*16*512 =  16,777,216 : Here refresh_zone_stat_thresholds
> > > takes around 4.5 seconds total for all the CPUs in the system under test.
> > 
> > Did you measure the overall before-and-after times?  IOW, how much of
> > that 4.5s do we reclaim?
> 
> This entire gain is accounted in over all boot processi time. Most of the Linux
> kernel boot process is sequential and doesn't take advantage of SMP.

Again, if you were able to measure 4.5s without the patch then you are
able to measure how long this delay is with the patch.  Please share
that number.