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Re: [PATCH] ARM: socfpga: add smp_ops.cpu_kill to make kexec/kdump available

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  Re: [PATCH] ARM: socfpga: add smp_ops.cpu_kill to make kexec/kdump  available Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com> - 2015-06-03 01:50 +0200
    Re: [PATCH] ARM: socfpga: add smp_ops.cpu_kill to make kexec/kdump  available Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-06-03 02:00 +0200

#1156987 — Re: [PATCH] ARM: socfpga: add smp_ops.cpu_kill to make kexec/kdump available

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)

Best regards,
Hiraku Toyooka
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#1156989

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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