linux-kernel - Re: [RFC/PATCH] Prevent wasting time to find out get_parent

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Date:	Wed, 25 Apr 2012 12:21:36 +0900
From:	Minho Ban <mhban@...sung.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Turner <pjt@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC/PATCH] Prevent wasting time to find out get_parent_ip

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.

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