linux-kernel - Re: [PATCH] Do not force shutdown/reboot to boot cpu.

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Message-ID: <5162EC1A.4050204@zytor.com>
Date:	Mon, 08 Apr 2013 09:11:06 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Robin Holt <holt@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Russ Anderson <rja@....com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] Do not force shutdown/reboot to boot cpu.

On 04/08/2013 08:57 AM, Ingo Molnar wrote:
> 
> I think the original commit:
> 
>   f96972f2dc63 kernel/sys.c: call disable_nonboot_cpus() in kernel_restart()
> 
> actually regressed your 1024 CPU systems, and should possibly be reverted or fixed 
> in some other fashion - such as by migrating to the primary CPU (on architectures 
> that require that), instead of hotplug offlining every secondary CPU on every 
> architecture!
> 
> Alternatively, disable_nonboot_cpus() could perhaps be improved to down CPUs in 
> parallel: issue the CPU-down requests to every CPU, then wait for them to complete 
> - instead of the loop over every CPU?
> 
> This would be the conceptual counter part to parallel boot up of CPUs - something 
> SGI might be interested in as well?
> 

Migrating to the boot processor and then calling stop_machine() to
defang any other processors should be sufficient, no?

I don't know if there is any reason to deschedule all tasks?

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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