On Tue, Apr 16, 2013 at 2:56 AM, Igor Stasenko <siguc...@gmail.com> wrote:
> On 16 April 2013 11:32, Henrik Johansen <henrik.s.johan...@veloxit.no> > wrote: > > > > On Apr 15, 2013, at 4:50 PM, Igor Stasenko wrote: > > > >> On 15 April 2013 16:43, Igor Stasenko <siguc...@gmail.com> wrote: > >>> On 15 April 2013 16:32, Henrik Johansen <henrik.s.johan...@veloxit.no> > wrote: > >>>> > >>>> On Apr 15, 2013, at 3:25 PM, Igor Stasenko wrote: > >>>> > >>>>> On 15 April 2013 12:14, Henrik Johansen < > henrik.s.johan...@veloxit.no> wrote: > >>>>>> > >>>>>> On Apr 13, 2013, at 12:16 AM, Igor Stasenko wrote: > >>>>>> > >>>>>>> > >>>>>>> But that's fine.. now look at > >>>>>>> > >>>>>>> secondsWhenClockTicks > >>>>>>> > >>>>>>> "waits for the moment when a new second begins" > >>>>>>> > >>>>>>> | lastSecond | > >>>>>>> > >>>>>>> lastSecond := self primSecondsClock. > >>>>>>> [ lastSecond = self primSecondsClock ] whileTrue: [ (Delay > >>>>>>> forMilliseconds: 1) wait ]. > >>>>>>> > >>>>>>> ^ lastSecond + 1 > >>>>>>> > >>>>>>> that is complete nonsense. Sorry. > >>>>>>> > >>>>>>> This code relying on primSecondsClock resolution, which is..... > (drum > >>>>>>> roll..... ) > >>>>>>> 1 second.. > >>>>>>> > >>>>>>> then it is combined with millisecondClockValue , as you see later > to get > >>>>>>> system time with millisecond precision.. > >>>>>>> > >>>>>>> I am not genius in math and physics.. but even i understand that if > >>>>>>> you measurement has error X > >>>>>>> you cannot get more precision than X, even if you combine it with > >>>>>>> another measurement with higher precision. > >>>>>>> > >>>>>>> (But i can be wrong with that.. if so, please explain why) > >>>>>> > >>>>>> Because, as Levente said in code, resolution != accuracy. > >>>>>> When you measure a single sample, sure, that value has an error of > max resolution / 2. > >>>>>> But when you measure when that value _changes_, you have an error > of the underlying accuracy / 2. > >>>>>> Clock s value: 1 2 > >>>>>> resolution: |_______|_______| > >>>>>> accuracy: ||||||||||||||||||||||||||||||||||| > >>>>>> ^ > >>>>>> Here's to hoping the above ascii art(?) worked! > >>>>>> > >>>>>> So no, that method is not complete nonsense. > >>>>>> > >>>>> Okay. > >>>>> Now i rewriting the code which uses new primitive > (primUTCMicrosecondClock), > >>>>> and then we will no longer need this startup logic nor wrap around > >>>>> check & other gory details... > >>>>> just use a primitive. > >>>> > >>>> Sounds clearer, yes. > >>>> > >>>> However, be aware, at least on my VM: > >>>> [Time millisecondClockValue] bench '34,600,000 per second.' > >>>> [Time primUTCMicrosecondClock] bench '12,400,000 per second.' > >>>> > >>>> Which in my case translated to that in a Time2 class with #now > defined: > >>>> now > >>>> > >>>> | microSecondsToday | > >>>> microSecondsToday := self primUTCMicrosecondClock \\ > 86400000000. > >>>> ^ self seconds: microSecondsToday // 1000000 nanoSeconds: > microSecondsToday * 1000 > >>>> > >>>> and changing the relatively low-hanging fruit in standard Time > (removing Duration creation and other crap): > >>>> > >>>> seconds: seconds nanoSeconds: nanoCount > >>>> "Answer a Time from midnight." > >>>> > >>>> ^ self basicNew > >>>> seconds: seconds nanoSeconds: nanoCount > >>>> > >>>> To benchmarks that looked like this: > >>>> "Old code" > >>>> [Time now ] bench '7,330,000 per second.' '7,280,000 per second.' > '7,170,000 per second.' > >>>> "Using microsecondClock every call" > >>>> [Time2 now ] bench '2,280,000 per second.''2,300,000 per second.' > '2,180,000 per second.' > >>>> > >>>> Also note, Time2 lacked translation to Local time, which would be > needed for consistency with Time now. > >>>> > >>> > >>> Well, i am not started modifying Time now, (will start in couple > minutes ;) > >>> but here results of DateAndTime now > >>> before and after: > >>> > >>> before: > >>> > >>> > >>> [ DateAndTime now ] bench '316,000 per second.' > >>> > >>> after: > >>> > >>> [ DateAndTime now ] bench '414,000 per second.' > >>> > >>> > >>> with Time now, i think even if it will be "2,300,000" answers per > second, > >>> it is fairly acceptable , when accuracy of primitive is 1 microsecond, > >>> you actually don't need more than 1 million answers per second, or you > >>> will receive same answers. > >>> > >>> But aside of it, may i ask, why performance is so important/critical > >>> for those? What is use case? > >>> > >> > >> everything is good in comparison: > >> > >> [ self yourself ] bench '58,800,000 per second.' > >> > >> does nothing and just 25 times faster.. than Time now, > >> so what is the point? :) > > > > The point was raising awareness that performance differences are also > worthy of measuring when doing a reimplementation, not just code > cleanliness. > > A 3x decrease in performance is worth at least consideration as part of > a reimplementation, even when the conclusion is "it's plenty fast enough > for most uses anyways". > > > > Not to mention, "Made X Y% faster" looks better in the release notes > than "Restructured the internals of X" :) > > > RIght. > So, it is 3x slower , 1000x more accurate (milli vs micro), do not > requires startup code > do not need to account for counter wrapping and day change => much > cleaner and nicer. > + less buggy. > As to me , the choice is obvious. > and when we implement a proper 64-bit system with e.g. 61-bit SmallIntegers it will no longer be 3 times slower :) > > > Cheers, > > Henry > > > > > > > > -- > Best regards, > Igor Stasenko. > > -- best, Eliot
