linux-kernel - Re: [patch 00/10] cpu/hotplug: Final cleanup

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Date:   Tue, 27 Dec 2016 20:41:53 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [patch 00/10] cpu/hotplug: Final cleanup

> > Just curious - what is the stage TWO (and onwards) plan?
> > lwn had some coverage of this work but I assume the
> > article is somewhat outdated.
> 
> Stage 2 is to consolidate all the archictecture code, i.e. reduce it to
> really arch specific callbacks and keep all the other things
> (synchronization, state settings etc.) in the core code.
> 
> After that we can do smart things like speed up the boot hotplug process:
> 
> prepare CPU1
> kick CPU1
> 
> prepare CPU2
> kick CPU2
> 
> ....
> 
> prepare CPUN
> kick CPUN
> 
> check CPU1 alive
> bringup CPU1
> 
> ...
> 
> check CPUN alive
> bringup CPUN
> 
> That saves ~200ms per CPU on x86, which we now spend busy waiting for the
> CPU to come alive.
> 
> There is more stuff which we can do in the long run like synchrounosly
> letting CPUs bring up themself after the basic init/sync checks, but that
> needs lot of surgery all over the place.

Thanks for the update - looking forward to follow this great clean-up!

	Sam