[PATCH v4] cpuidle: Fix last_residency division

Shreyas B Prabhu shreyas at linux.vnet.ibm.com
Sat Jul 2 00:16:35 AEST 2016

On 07/01/2016 01:36 PM, Daniel Lezcano wrote:
> On 06/30/2016 05:37 PM, Nicolas Pitre wrote:
>> On Thu, 30 Jun 2016, Daniel Lezcano wrote:
>>> +    }
>>>> +}
>>> What bothers me with this division is the benefit of adding an extra
>>> ultra
>>> optimized division by 1000 in cpuidle.h while we have already
>>> ktime_divns
>>> which is optimized in ktime.h.
>> It is "optimized" but still much heavier than what is presented above as
>> it provides maximum precision.
>> It all depends on how important the performance gain from the original
>> shift by 10 was in the first place.
> Actually the original shift was there because it was convenient as a
> simple ~div1000 operation. But against all odds, the approximation
> introduced a regression on a very specific use case on PowerPC.
> We are not in the hot path and I think we can live with a ktime_divns
> without problem. That would simplify the fix I believe.

I agree too. I'll post next version with this.


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