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

From: Daniel Lezcano
Date: Wed Apr 15 2015 - 08:50:47 EST

On 04/15/2015 02:42 PM, Peter Zijlstra wrote:
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());


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.

Ok. I was trying to save one variable on the stack by reusing the idle_stamp value but if we store it in a different unit, then we have to keep it in order to have usecond for the governors.

I was thinking about converting to nanosecond the cpuidle framework but it is not worth to do that as the resolution is too high for the idle states.

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