Re: linux-next: build failure

Mike Travis
2008-07-29T14:32:04Z

Ingo Molnar wrote:
> * KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
>
>>> * Stephen Rothwell <sfr@canb.auug.org.au> wrote:
>>>
>>>> Hi Ingo,
>>>>
>>>> On Tue, 29 Jul 2008 10:00:55 +0200 Ingo Molnar <mingo@elte.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