linux-kernel - Re: [PATCH 1/3] cpuidle: Store the idle start time stamp

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Message-ID: <20150415124246.GW5029@twins.programming.kicks-ass.net>
Date:	Wed, 15 Apr 2015 14:42:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	rjw@...ysocki.net, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, nicolas.pitre@...aro.org
Subject: Re: [PATCH 1/3] cpuidle: Store the idle start time stamp

On Wed, Apr 15, 2015 at 02:29:06PM +0200, Daniel Lezcano wrote:
> On 04/15/2015 12:20 PM, Peter Zijlstra wrote:
> >On Wed, Apr 15, 2015 at 12:00:22PM +0200, Daniel Lezcano wrote:
> >>+	target_state->idle_stamp = ktime_to_us(ktime_get());
> >
> >ktime_get_ns();
> >
> 
> Hmm, sounds like I missed we are dealing with different units (us / ns) in
> cpuidle / sched.
> 
> Would it make sense to store the time into a ktime structure instead and use
> the relevant function depending on the place we are inspecting the value
> from ?

Why would you ever want to use us? Does ARM enjoy calculating /1000?

Ah, I see the !scalar ktime got whacked, good! At which point the u64 ns
and ktime are the same. That said I prefer the u64 over ktime because
its easier to manipulate.

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