Re: API explosion (Re: [RFC/RFT] calloutng)

On 19.12.2012 01:37, Ian Lepore wrote:
> On Wed, 2012-12-19 at 00:29 +0100, Luigi Rizzo wrote:
>> On Tue, Dec 18, 2012 at 04:27:45PM -0700, Ian Lepore wrote:
>>> On Tue, 2012-12-18 at 23:58 +0100, Luigi Rizzo wrote:
>>>> [top posting for readability;
>>>> in summary we were discussing the new callout API trying to avoid
>>>> an explosion of methods and arguments while at the same time
>>>> supporting the old API and the new one]
>>>> (I am also Cc-ing phk as he might have better insight
>>>> on the topic).
>>>>
>>>> I think the patch you propose is a step in the right direction,
>>>> but i still remain concerned by having to pass two bintimes
>>>> (by reference, but they should really go by value)
>>>> and one 'ticks' value to all these functions.
>>>>
>>>> I am also dubious that we need a full 128 bits to specify
>>>> the 'precision': there would be absolutely no loss of functionality
>>>> if we decided to specify the precision in powers of 2, so a precision
>>>> 'k' (signed) means 2^k seconds. This way 8 bits are enough to
>>>> represent any precision we want.
>>
>> ...
>>> I'm not so sure about the 2^k precision.  You speak of seconds, but I
>>> would be worrying about sub-second precision in my work.  It would
>>> typical to want a 500uS timeout but be willing to late by up to 250uS if
>>
>> i said k is signed so negative values represent fractions of a
>> second. 2^-128 is pretty short :)
>
> Ahh, I missed that.  Good enough then!  Hmmm, if that ideas survives
> further review, then could precision be encoded in 8 bits of the flags,
> eliminating another parm?

Those who tracked the branch could see that actually was our first 
approach to handle precision. Unfortunately, it appeared not very 
convenient when you need to convert relative precision in percents or 
fraction of interval to the absolute precision in power of 2. We were 
worried that using some ffsll() for it can be inconvenient or expensive. 
But since we are now talking about passing relative bintime as an 
argument, that may be more viable option. I'll make another try.

Thanks for the input. Pity it didn't happen couple of months ago.

-- 
Alexander Motin