linux-kernel - Re: [PATCH 07/25] hrtimer: Reduce conditional code (hres

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Message-ID: <20170925135542.sc4czjbb2j3s5jsj@hirez.programming.kicks-ass.net>
Date:   Mon, 25 Sep 2017 15:55:42 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Christoph Hellwig <hch@....org>, keescook@...omium.org,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 07/25] hrtimer: Reduce conditional code (hres_active)

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?