linux-kernel - Re: [PATCH -v2 5/5] x86: use dmi check to treat disabled cpus as hotplug cpus.

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Message-ID: <4B4D2F49.6070509@kernel.org>
Date:	Tue, 12 Jan 2010 18:26:17 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"ananth@...ibm.com" <ananth@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -v2 5/5] x86: use dmi check to treat disabled cpus as
 hotplug cpus.

On 01/12/2010 06:21 PM, Suresh Siddha wrote:
> On Tue, 2010-01-12 at 18:13 -0800, Yinghai Lu wrote:
>> On 01/12/2010 06:06 PM, Suresh Siddha wrote:
>>> On Tue, 2010-01-12 at 17:55 -0800, Yinghai Lu wrote:
>>>> you mean this blacklist could be too long?
>>>
>>> yes.
>>>
>>>>
>>>> switch to whitelist for the box can treat disabled cpus as hotplug
>>>> cpus?
>>>
>>> Do we really need all this? Systems which support physical hotplug
>>> typically have lot's of cpu's (mostly will have atleast > 8). Even if we
>>> really need to identify, then perhaps we can check if ACPI has any hints
>>> regarding the physical hotplug support at boot time (we should check
>>> with Andi Kleen or Len Brown on this).
>>>
>>> For now, I think we can keep it simple by using the detected enabled
>>> cpu's.
>>
>> sth like this ?
> 
> Well, I was referring more to the apic model selection than the prefill
> case. About this possible cpu's, will the wastage be more than few kb
> for few disabled cpu's.

for 8 sockets systems if only have two cpus instatalled.

that disabled cpus will be 6 * 8 * 2 = 96.

and per_cpu area is about per cpu 2M, so will waste about 96 x 2M

YH
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