Re: hotplug support for arch/arc/plat-eznps platform

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: hotplug support for arch/arc/plat-eznps platform
Date	2017-08-07 17:20 +0200
Message-ID	<ubRZ0-1OG-25@gated-at.bofh.it> (permalink)
References	<ubmLv-6Is-1@gated-at.bofh.it> <ubLJU-5RE-9@gated-at.bofh.it> <ubQzU-s0-17@gated-at.bofh.it>
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On Mon, Aug 07, 2017 at 01:41:38PM +0000, Ofer Levi(SW) wrote:
> > 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.

But who is doing actual hotplug? Why would you ever unplug or plug a CPU
in a time critical situation?

> > 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.

Doesn't make sense. If you look at smp_init() boot brings up the CPUs
one at a time.

So how can boot be different than hot-pugging them?

Thread

hotplug support for arch/arc/plat-eznps platform "Ofer Levi(SW)" <oferle@mellanox.com> - 2017-08-06 08:00 +0200
  Re: hotplug support for arch/arc/plat-eznps platform Peter Zijlstra <peterz@infradead.org> - 2017-08-07 10:40 +0200
    RE: hotplug support for arch/arc/plat-eznps platform "Ofer Levi(SW)" <oferle@mellanox.com> - 2017-08-07 15:50 +0200
      Re: hotplug support for arch/arc/plat-eznps platform Peter Zijlstra <peterz@infradead.org> - 2017-08-07 17:20 +0200
        RE: hotplug support for arch/arc/plat-eznps platform "Ofer Levi(SW)" <oferle@mellanox.com> - 2017-08-08 08:50 +0200
          Re: hotplug support for arch/arc/plat-eznps platform Peter Zijlstra <peterz@infradead.org> - 2017-08-08 12:20 +0200
            RE: hotplug support for arch/arc/plat-eznps platform "Ofer Levi(SW)" <oferle@mellanox.com> - 2017-08-09 17:20 +0200
              Re: hotplug support for arch/arc/plat-eznps platform Peter Zijlstra <peterz@infradead.org> - 2017-08-09 17:40 +0200
                RE: hotplug support for arch/arc/plat-eznps platform "Ofer Levi(SW)" <oferle@mellanox.com> - 2017-08-10 09:50 +0200
                Re: hotplug support for arch/arc/plat-eznps platform Peter Zijlstra <peterz@infradead.org> - 2017-08-10 11:20 +0200
                RE: hotplug support for arch/arc/plat-eznps platform "Ofer Levi(SW)" <oferle@mellanox.com> - 2017-08-10 14:00 +0200
                Re: hotplug support for arch/arc/plat-eznps platform Peter Zijlstra <peterz@infradead.org> - 2017-08-10 17:50 +0200

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