linux-kernel - Re: [PATCH] ARM: socfpga: add smp_ops.cpu

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Date:	Wed, 3 Jun 2015 00:52:39 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Hiraku Toyooka <hiraku.toyooka.gu@...achi.com>
Cc:	dinguyen@...nsource.altera.com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: socfpga: add smp_ops.cpu_kill to make kexec/kdump
 available

On Wed, Jun 03, 2015 at 08:40:51AM +0900, Hiraku Toyooka wrote:
> Hello, Russell,
> 
> On 2015/06/02 17:38, Russell King - ARM Linux wrote:
> > I wasn't thinking of SPIs and PPIs, but SGIs - the IPI interrupts coming
> > from the boot CPU.
> 
> All tasks in a CPU going offline are migrated to other CPUs(finally
> CPU0) and the rq is marked with offline before the CPU entering WFI
> loop. So IPI is not sent to the secondary CPU.
> 
> > If you have a way to reset CPU0, why are you not using this for hotplug
> > when a CPU is hot-unplugged?
> 
> I think you mean "way to reset CPU1". If so, the reason is an increase
> in power consumption in usual hotplug. This is discussed before between
> Alan Tull and you. (https://lkml.org/lkml/2014/9/25/37)

Please put a comment in your hotplug code describing this, so I'm
not likely to ask again (and I don't have to remember that I've
asked the question.)  Thanks.

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