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

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Message-ID: <50AD2D16.7050304@oracle.com>
Date:	Wed, 21 Nov 2012 14:35:50 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, penberg@...nel.org
Subject: Re: [PATCH] x86, smpboot: allow manual hotplug of CPUs

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?


Thanks,
Sasha
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