linux-kernel - Re: smp: Start up non-boot CPUs asynchronously

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Message-ID: <20120131054155.371e8307@infradead.org>
Date:	Tue, 31 Jan 2012 05:41:55 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, Milton Miller <miltonm@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	arjanvandeven@...il.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: smp: Start up non-boot CPUs asynchronously

On Tue, 31 Jan 2012 13:52:32 +0100
Ingo Molnar <mingo@...e.hu> wrote:
> 
> The real fix would be to make the init code depend less on each 
> other, i.e. have less hotplug lock dependencies. Or, if it's 
> such a hot lock for a good reason, why does spinning on it slow 
> down the boot process? It really shouldnt.

by inspection, anything that calls get_online_cpus()/put_online_cpus()
will block while a CPU is coming up. This is used in things like 
kmem_cache_create()... which is used about everywhere.
(there's various other places... more or less it's a requirement
for using the for_each_online_cpu() api correctly)



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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