linux-kernel - Re: linux-next: build failure

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Message-ID: <488F29D5.1080105@sgi.com>
Date:	Tue, 29 Jul 2008 07:31:49 -0700
From:	Mike Travis <travis@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	David Miller <davem@...emloft.net>, linux-next@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus <torvalds@...ux-foundation.org>
Subject: Re: linux-next: build failure

Ingo Molnar wrote:
> * KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> 
>>> * Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>>>
>>>> Hi Ingo,
>>>>
>>>> On Tue, 29 Jul 2008 10:00:55 +0200 Ingo Molnar <mingo@...e.hu> wrote:
>>>>>> -#define cpumask_of_cpu(cpu) ({ *get_cpu_mask(cpu); })
>>>>>> +#define cpumask_of_cpu(cpu) (*get_cpu_mask(cpu))
>>>>> hm, i'm wondering - is this a compiler bug?
>>>> Or maybe a deficiency in such an old compiler (v3.4.5) but the fix 
>>>> makes sense anyway, right?
>>> yeah, i was just wondering.
>> in linux/README
>>
>> COMPILING the kernel:
>>
>>  - Make sure you have at least gcc 3.2 available.
>>    For more information, refer to Documentation/Changes.
>>
>> So, if 3.4.5 is old, Should we change readme?
> 
> the fix is simple enough.
> 
> but the question is, wont it generate huge artificial stackframes with 
> CONFIG_MAXSMP and NR_CPUS=4096? Maybe it is unable to figure out and 
> simplify the arithmetics there - or something like that.
> 
> 	Ingo

I've looked at stack frames quite extensively and usually they are
not generated unless you explicitly use a named cpumask variable,
pass a cpumask by value, expect a cpumask function return, create
an initializer that contains a cpumask field, and (probably a couple
more I missed).

Almost all others are done efficiently via pointers or simple
struct copies:

	cpus_xxx(*cpumask_of_cpu(), ...
	struct->cpumask_var = *cpumask_of_cpu()
	global_cpumask_var = *cpumask_of_cpu()
	etc.

Thanks,
Mike
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