linux-kernel - Re: [PATCH] x86: allow 8 more cpus could be used

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Date:	Fri, 30 Jan 2009 01:09:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Yinghai Lu <yinghai@...nel.org>,
	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] x86: allow 8 more cpus could be used


* Randy Dunlap <randy.dunlap@...cle.com> wrote:

> Ingo Molnar wrote:
> > * Randy Dunlap <randy.dunlap@...cle.com> wrote:
> > 
> >> Ingo Molnar wrote:
> >>> * Randy Dunlap <randy.dunlap@...cle.com> wrote:
> >>>
> >>>> Ingo Molnar wrote:
> >>>>> * Yinghai Lu <yinghai@...nel.org> wrote:
> >>>>>
> >>>>>> Impact: fix left out MARCO
> >>>>>>
> >>>>>> X86_PC will be always enabled. so need to check if we have bigsmp 
> >>>>>> support built in before cut off more than 8 cpus.
> >>>>> ah, that's a leftover reference to X86_PC. It can now be removed, together 
> >>>>> with the Kconfig X86_PC option.
> >>>>>
> >>>>>> -#if defined(CONFIG_X86_PC) && defined(CONFIG_X86_32)
> >>>>>> +#if defined(CONFIG_X86_PC) && !defined(CONFIG_X86_BIGSMP)
> >>>>>>  	if (def_to_bigsmp && nr_cpu_ids > 8) {
> >>>>>>  		unsigned int cpu;
> >>>>>>  		unsigned nr;
> >>>>> Could you please send a patch that removes both X86_PC and X86_BIGSMP - 
> >>>>> and removes the above cutoff code too, so that it will be built-in all the 
> >>>>> time?
> >>>> and at what cost, please?
> >>> the size difference between a bigsmp and a normal-smp x86 defconfig kernel 
> >>> is 0.011%. Zero difference on a UP kernel. (And UP is what most of the 
> >>> ultra-embedded systems are using)
> >> That's static size?  how about cpu and apic table space?
> > 
> > What do you mean? What is your point and what is your exact question?
> 
> There used to be large CPU and APIC tables (depending on the MAX number 
> of these devices that are supported in a kernel).  Are those gone?

ah, ok. No, there's no such dependency on CONFIG_X86_BIGSMP. The total 
size difference is around 900 bytes on the defconfig kernel - and that 
includes the APIC tables too.

> If not, then I agree with YH and CONFIG_BIGSMP is still needed/wanted by 
> small systems.

It's not a size issue - but we can still keep the option.

	Ingo
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