From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1758123Ab2DXXp2 (ORCPT <rfc822;w@1wt.eu>);
	Tue, 24 Apr 2012 19:45:28 -0400
Received: from relay3-d.mail.gandi.net ([217.70.183.195]:46848 "EHLO
	relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753653Ab2DXXp1 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 24 Apr 2012 19:45:27 -0400
X-Originating-IP: 217.70.178.131
X-Originating-IP: 50.43.46.74
Date: Tue, 24 Apr 2012 16:45:14 -0700
From: Josh Triplett <josh@joshtriplett.org>
To: Minho Ban <mhban@samsung.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        Frederic Weisbecker <fweisbec@gmail.com>, Paul Turner <pjt@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [RFC/PATCH] Prevent wasting time to find out get_parent_ip
Message-ID: <20120424234513.GA11841@leaf>
References: <4F969E53.9080307@samsung.com>
 <1335272025.28150.193.camel@twins>
 <4F9737CC.6010703@samsung.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4F9737CC.6010703@samsung.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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