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Date: Mon, 08 Apr 2013 09:11:06 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Ingo Molnar <mingo@kernel.org>
CC: Robin Holt <holt@sgi.com>, Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Russ Anderson <rja@sgi.com>,
        Shawn Guo <shawn.guo@linaro.org>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] Do not force shutdown/reboot to boot cpu.
References: <20130403193743.GB29151@sgi.com> <20130408155701.GB19974@gmail.com>
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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.