linux-kernel - Re: Possible bug in 2.6.34 slub

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Message-ID: <AANLkTinxOJShwd7xUornVI89BmJnbX9-a7LVWaciNdr5@mail.gmail.com>
Date:	Thu, 3 Jun 2010 09:51:41 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Randy Dunlap <rdunlap@...otime.net>,
	Giangiacomo Mariotti <gg.mariotti@...il.com>,
	Bill Davidsen <davidsen@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, x86 maintainers <x86@...nel.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: Possible bug in 2.6.34 slub

On Tue, Jun 1, 2010 at 10:48 PM, Christoph Lameter
<cl@...ux-foundation.org> wrote:
> On Tue, 1 Jun 2010, Randy Dunlap wrote:
>
>> > >>> My cpu is an I7 920, so it has 4 cores and there's hyperthreading
>> > >>> enabled, so there are 8 logical cpus. Is this a bug?
>
> Yes its a bug in the arch code or BIOS. The system configuration tells us
> that there are more possible cpus and therefore the system prepares for
> the additional cpus to be activated at some later time.

I guess we should CC x86 maintainers then!

>> Sorry, I think that I misread your report.
>> It does look like misinformation.
>> Let's cc Christoph Lameter & Pekka.
>>
>>
>> > The point is, I guess(didn't actually look at the code), if that's
>> > just the count of MAX number of cpus supported, which is a config time
>> >  define and then the actual count gets refined afterwards by slub
>> > too(because I know that the rest of the kernel knows I've got 4
>> > cores/8 logical cpus) or not. Is that it? If this is not the case(that
>> > is, it's not a static define used as a MAX value), then I can't see
>> > what kind of boot/init time info it is. If it's a boot-time info, it
>> > just means it's a _wrong_ boot-time info.
>
> No that is the max nr of cpus possible on this machine. The count is
> determined by hardware capabilities on bootup. If they are not detected
> in the right way then you have the erroneous display (and the system
> configures useless per cpu structures to support nonexistent cpus).
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