Re: [RFC/PATCH] Prevent wasting time to find out get_parent_ip

[Minho Ban <mhban@samsung.com>]

On 04/25/2012 08:45 AM, Josh Triplett wrote:
> On Wed, Apr 25, 2012 at 08:31:24AM +0900, Minho Ban wrote:
>> On 04/24/2012 09:53 PM, Peter Zijlstra wrote:
>>> On Tue, 2012-04-24 at 21:36 +0900, Minho Ban wrote:
>>>> trace_preempt_on/off looks empty if PREEMPT_TRACER is off. But actually it is
>>>> spending time to find out get_parent_ip(even CALLER_ADDR for some ARCH) which is
>>>> in argument. This seems not fair for those who expect to do nothing but increase
>>>> or decrease count.
>>>
>>> You can do the same by making them CPP macros and adding a comment as to
>>> why they're macros instead of inlines..
>>>
>>
>> Thank you for pointing this out, certainly macros look better. I'll amend this.
> 
> As an alternative, how about making get_parent_ip and its called
> functions static inlines?  Then the compiler can eliminate them via dead
> code elimination.
> 
> Or, how about declaring get_parent_ip with the GCC "pure" attribute?
> That would tell GCC that it can safely eliminate calls to the function.
> 
> - Josh Triplett
> 

Thank you for alternative method, but I'm afraid this could not cover the CALLER_ADDR.