Subject: Re: [PATCH v3] cpuidle: Fix last_residency division

From: Shreyas B Prabhu <[email-masked]>
Date: Thu, 30 Jun 2016 19:50:03 +0530

On 06/29/2016 08:31 PM, Nicolas Pitre wrote:
> On Wed, 29 Jun 2016, Daniel Lezcano wrote:
> 
>> On 06/29/2016 09:06 AM, Shreyas B. Prabhu wrote:
>>> diff --git a/drivers/cpuidle/cpuidle.h b/drivers/cpuidle/cpuidle.h
>>> index f87f399..c8ea5ad 100644
>>> --- a/drivers/cpuidle/cpuidle.h
>>> +++ b/drivers/cpuidle/cpuidle.h
>>> @@ -68,4 +68,27 @@ static inline void
>>> cpuidle_coupled_unregister_device(struct cpuidle_device *dev)
>>>   }
>>>   #endif
>>>
>>> +/*
>>> + * Used for calculating last_residency in usec. Optimized for case
>>> + * where last_residency in nsecs is < INT_MAX/2 by using faster
>>> + * approximation. Approximated value has less than 1% error.
>>> + */
>>> +static inline int convert_nsec_to_usec(u64 nsec)
>>> +{
>>> +	if (likely(nsec < INT_MAX / 2)) {
>>
>> UINT_MAX ?
> 
> Actually this can be better than that.
> 
>>> +		int usec = (int)nsec;
> 
> First, you'll want an unsigned type. Given the provided argument is u64, 
> we can assume there won't be any negative values here.
> 
> Then it would be wise to use a type with an explicit width, like U32.

Cool. I wanted to avoid multiple casts. i.e u64 -> u32 -> int. But I
guess there is no real need to avoid it.

Sending v4 with your suggestions.

Thanks,
Shreyas