linux-kernel - Re: [PATCH] x86, smpboot: allow manual hotplug of CPUs

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Date:	Wed, 21 Nov 2012 11:39:07 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Sasha Levin <sasha.levin@...cle.com>
CC:	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, penberg@...nel.org,
	"Brown, Len" <len.brown@...el.com>
Subject: Re: [PATCH] x86, smpboot: allow manual hotplug of CPUs

On 11/21/2012 11:35 AM, Sasha Levin wrote:
> On 11/21/2012 02:24 PM, H. Peter Anvin wrote:
>> On 11/21/2012 11:19 AM, Sasha Levin wrote:
>>>>
>>>> So, are there any mptables platforms which support hotplug?  If the
>>>> answer is "KVM" then the answer is that KVM needs to move to ACPI to get
>>>> the proper functionality; putting a hack in is really not okay.
>>>
>>> There are no platforms which support actual hotplug, but you can still set
>>> existing processors as disabled in the table and without this patch there's
>>> no way enable them.
>>>
>>> I'm not sure if it's a "hack" though - the presentation of hotpluggable cpus
>>> is the almost the same between mptable and acpi, and acpi provides a way to
>>> manually probe/release cpus as well. The only difference is that acpi also
>>> provides notifications about such events.
>>>
>>> Actually, maybe acpi should start using probe/release as well... hmm...
>>>
>>
>> The bottom line is that I don't want the underlying implementation to
>> end up with a user-visible difference... therein lies madness and lots
>> of bugs.
> 
> Okay, so if in the case of ACPI, 'probe' will call acpi_processor_add()
> and 'release' would call acpi_processor_remove() so the behaviour
> would be the same for both ACPI and mptables. Is this okay?
> 

Sounds reasonable to me.  Adding Len to the Cc: list.

	-hpa


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