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    SubjectRe: [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@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.

    thanks,
    Chenyu

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