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SubjectRE: hotplug support for arch/arc/plat-eznps platform
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> You've failed to explain why you think hotplug should be a performance
> critical path.
1. hotplug bring up of 4K cpus takes 40 minutes. Way too much for any user.
2. plat-eznps is a network processor, where bring up time is sensitive.

> I'm also not seeing how it would be different from boot; you'd be
> looking at a similar cost for SMP bringup.
bring up time of 4k cpus during kernel boot takes 4.5 minutes.
The function in question is performed only when smp init was performed.
If I understand correctly, whatever this function is doing is performed after all cpus
were brought up during kernel boot.


Thanks
-Ofer


On Monday, August 7, 2017 11:34 AM +0000, Peter Zijlstra wrote:
> On Sun, Aug 06, 2017 at 05:53:37AM +0000, Ofer Levi(SW) wrote:
> > I'm adding hot-plug support for the above arch and ran into performance
> issue with execution of
> > partition_sched_domains () - About 0.5 sec per cpu, which is unacceptable
> with the arch supported 4k cpus.
> > To my limited understanding, on the plat-eznps arch, where each cpu is
> always running a single threaded process in
> > isolation mode, the above call is not necessary,
> > Can you please confirm (or reject) my understanding? If I'm wrong short
> explanation will be appreciated.
> > If I'm correct, I will be grateful if you can point me to how to skip this call in
> a way acceptable by community.
>
> You've failed to explain why you think hotplug should be a performance
> critical path.
>
> I'm also not seeing how it would be different from boot; you'd be
> looking at a similar cost for SMP bringup.

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