Re: [mm/migrate] 9eeb73028c: stress-ng.memhotplug.ops_per_sec -53.8% regression

[Huang, Ying]

Chen Yu <yu.c.chen@xxxxxxxxx> writes:

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