From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964974AbdIYO2L (ORCPT ); Mon, 25 Sep 2017 10:28:11 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:45205 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933355AbdIYO2K (ORCPT ); Mon, 25 Sep 2017 10:28:10 -0400 Date: Mon, 25 Sep 2017 16:28:07 +0200 (CEST) From: Thomas Gleixner To: Peter Zijlstra cc: Anna-Maria Gleixner , LKML , Ingo Molnar , Christoph Hellwig , keescook@chromium.org, John Stultz Subject: Re: [PATCH 07/25] hrtimer: Reduce conditional code (hres_active) In-Reply-To: <20170925135542.sc4czjbb2j3s5jsj@hirez.programming.kicks-ass.net> Message-ID: References: <20170831105725.809317030@linutronix.de> <20170831105826.120809106@linutronix.de> <20170925135542.sc4czjbb2j3s5jsj@hirez.programming.kicks-ass.net> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 25 Sep 2017, Peter Zijlstra wrote: > On Thu, Aug 31, 2017 at 12:23:36PM -0000, Anna-Maria Gleixner wrote: > > The hrtimer_cpu_base struct has the CONFIG_HIGH_RES_TIMERS conditional > > struct member hres_active. All related functions to this member are > > conditional as well. > > > > There is no functional change, when the hres_active member is unconditional > > with all related functions and is set to zero during initialization. This > > makes the code easier to read. > > But you make what was a compile time dead-code-elimination into a > runtime load-and-branch. > > Unless the compiler is overly clever and is able to deduce from the lack > of assignments that it must always be 0, is it? Probably not. So the simple way to solve this is to make the new common is_highres_active() { return IS_ENABLED(CONFIG_HIGH_RES) ? base->hres_active : 0; } Thanks, tglx