linux-kernel - Re: [PATCH] cpuidle: Change ktime_get() with local

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Message-ID: <20160420121315.GC3408@twins.programming.kicks-ass.net>
Date:	Wed, 20 Apr 2016 14:13:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	rjw@...ysocki.net, mingo@...nel.org,
	"open list:CPUIDLE DRIVERS" <linux-pm@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpuidle: Change ktime_get() with local_clock()

On Thu, Apr 14, 2016 at 09:23:54PM +0200, Daniel Lezcano wrote:
> @@ -217,7 +217,11 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
>  	if (!cpuidle_state_is_coupled(drv, entered_state))
>  		local_irq_enable();
>  
> -	diff = ktime_to_us(ktime_sub(time_end, time_start));
> +	/*
> +	 * local_clock() returns the time in nanosecond, let's shift
> +	 * by 10 (divide by 1024) to have microsecond based time.
> +	 */
> +	diff = (time_end - time_start) >> 10;

Changelog fails to explain the ramifications of this change...