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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Chen Yu <yu.c.chen@intel.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        kernel test robot <oliver.sang@intel.com>,
        Rui Zhang <rui.zhang@intel.com>,
        Len Brown <len.brown@intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        0day robot <lkp@intel.com>, "Yang Shi" <shy828301@gmail.com>,
        Zi Yan <ziy@nvidia.com>, Michal Hocko <mhocko@suse.com>,
        Wei Xu <weixugc@google.com>,
        Oscar Salvador <osalvador@suse.de>,
        David Rientjes <rientjes@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Greg Thelen <gthelen@google.com>,
        Keith Busch <kbusch@kernel.org>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        LKML <linux-kernel@vger.kernel.org>, <lkp@lists.01.org>,
        <feng.tang@intel.com>, <zhengjun.xing@linux.intel.com>,
        <dave.hansen@linux.intel.com>, <linux-mm@kvack.org>,
        <mm-commits@vger.kernel.org>, <torvalds@linux-foundation.org>
Subject: Re: [mm/migrate] 9eeb73028c: stress-ng.memhotplug.ops_per_sec
 -53.8% regression
References: <20210905135932.GE15026@xsang-OptiPlex-9020>
        <87y28aii58.fsf@yhuang6-desk2.ccr.corp.intel.com>
        <ee55e83e-d8bd-2888-3159-154706aa5173@intel.com>
        <87lf4ai6u3.fsf@yhuang6-desk2.ccr.corp.intel.com>
        <20210906060908.GA17483@chenyu5-mobl1>
Date:   Mon, 06 Sep 2021 16:31:41 +0800
In-Reply-To: <20210906060908.GA17483@chenyu5-mobl1> (Chen Yu's message of
        "Mon, 6 Sep 2021 14:09:08 +0800")
Message-ID: <874kayhzpu.fsf@yhuang6-desk2.ccr.corp.intel.com>
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Chen Yu <yu.c.chen@intel.com> writes:

> On Mon, Sep 06, 2021 at 01:57:56PM +0800, Huang, Ying wrote:
>> Dave Hansen <dave.hansen@intel.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.

Got it!  Thanks for your information.  Maybe we can try Dave's method
firstly and check whether that's OK for suspend/resume.

Best Regards,
Huang, Ying