linux-kernel - Re: [PATCH] x86: remove unused code in set_cyc2ns

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Date:	Thu, 31 Jan 2008 16:21:59 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Guillaume Chazarain <guichaz@...oo.fr>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: remove unused code in set_cyc2ns_scale()


* Guillaume Chazarain <guichaz@...oo.fr> wrote:

>  arch/x86/kernel/tsc_32.c |   14 +++++---------
>  arch/x86/kernel/tsc_64.c |   14 +++++---------
>  2 files changed, 10 insertions(+), 18 deletions(-)

>  static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
>  {
> -	unsigned long flags, prev_scale, *scale;
> -	unsigned long long tsc_now, ns_now;
> +	unsigned long flags, *scale;
> +
> +	if (!cpu_khz)
> +		return;
>  
>  	local_irq_save(flags);
>  	sched_clock_idle_sleep_event();
>  
>  	scale = &per_cpu(cyc2ns, cpu);
> -
> -	rdtscll(tsc_now);
> -	ns_now = __cycles_2_ns(tsc_now);
> -
> -	prev_scale = *scale;
> -	if (cpu_khz)
> -		*scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
> +	*scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;

hm, this is not a pure elimination of dead code, this will change 
behavior. For example we wont call sched_clock_idle_sleep_event() on 
!cpu_khz now. Hm?

	Ingo
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