linux-kernel - Re: [mm/migrate] 9eeb73028c: stress-ng.memhotplug.ops_per

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Date:   Mon, 6 Sep 2021 14:09:08 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        kernel test robot <oliver.sang@...el.com>,
        Rui Zhang <rui.zhang@...el.com>,
        Len Brown <len.brown@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        0day robot <lkp@...el.com>, Yang Shi <shy828301@...il.com>,
        Zi Yan <ziy@...dia.com>, Michal Hocko <mhocko@...e.com>,
        Wei Xu <weixugc@...gle.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Rientjes <rientjes@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Greg Thelen <gthelen@...gle.com>,
        Keith Busch <kbusch@...nel.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        feng.tang@...el.com, zhengjun.xing@...ux.intel.com,
        dave.hansen@...ux.intel.com, linux-mm@...ck.org,
        mm-commits@...r.kernel.org, torvalds@...ux-foundation.org
Subject: Re: [mm/migrate] 9eeb73028c: stress-ng.memhotplug.ops_per_sec -53.8%
 regression

On Mon, Sep 06, 2021 at 01:57:56PM +0800, Huang, Ying wrote:
> Dave Hansen <dave.hansen@...el.com> writes:
> 
> > On 9/5/21 6:53 PM, Huang, Ying wrote:
> >>> in testcase: stress-ng
> >>> on test machine: 96 threads 2 sockets Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz with 192G memory
> >>> with following parameters:
> >>>
> >>> 	nr_threads: 10%
> >>> 	disk: 1HDD
> >>> 	testtime: 60s
> >>> 	fs: ext4
> >>> 	class: os
> >>> 	test: memhotplug
> >>> 	cpufreq_governor: performance
> >>> 	ucode: 0x5003006
> >>>
> >> Because we added some operations during online/offline CPU, it's
> >> expected that the performance of online/offline CPU will decrease.  In
> >> most cases, the performance of CPU hotplug isn't a big problem.  But
> >> then I remembers that the performance of the CPU hotplug may influence
> >> suspend/resume performance :-(
> >> 
> >> It appears that it is easy and reasonable to enclose the added
> >> operations inside #ifdef CONFIG_NUMA.  Is this sufficient to restore the
> >> performance of suspend/resume?
> >
> > It's "memhotplug", not CPUs, right?
> 
> Yes.  Thanks for pointing that out!
> 
> We will update node_demotion[] in CPU hotplug too.  Because the status
> that whether a node has CPU may change after CPU hotplug.  And CPU
> online/offline performance may be relevant for suspend/resume.
>
Rui and I took a look at the default kernel config, it seems that CONFIG_NUMA is
enabled on laptops on some distributions. Maybe a runtime detecting flag indicating
that whether this system has enabled NUMA (static key eg) would be an option too, so as
not to enable node_demotion[] on non-NUMA laptops/desktops.

thanks,
Chenyu