`On Wednesday 17 July 2002 22:31, Richard B. Johnson wrote:> On Wed, 17 Jul 2002, Daniel Phillips wrote:> > > On Monday 15 July 2002 07:06, Linus Torvalds wrote:> > > There is, of course, the option to do variable frequency (and make it> > > integer multiples of the exposed "constant HZ" so that kernel code> > > doesn't actually need to _care_ about the variability). There are> > > patches to play with things like that.> > > > We don't have to feel restricted to integer multiples.  I'll paste in my > > earlier post, for your convenience:> > > > > ...If somebody wants a cruder scheduling interval than the raw timer> > > interrupt, that's child's play, just step the interval down.  The> > > only slightly challenging thing is do that without restricting> > > choice of rate for the raw timer and scheduler, respectively.  Here,> > > a novel application of Bresenham's algorithm (the line drawing> > > algorithm) works nicely: at each raw interrupt, subtract the period> > > of the raw interrupt from an accumulator; if the result is less> > > than zero, add the period of the scheduler to the accumlator and> > > drop into the scheduler's part of the timer interrupt.> > > > [which just increments the timer variable I believe]> > > > > This Bresenham trick works for arbitrary collections of interrupt> > > rates, all with different periods.  It has the property that,> > > over time, the total number of invocations at each rate remains> > > *exactly* correct, and so long as the raw interrupt runs at a> > > reasonably high rate, displacement isn't that bad either.> > > > This technique is scarcely less efficient than the cruder method.> > It is hardly novel and I can't imagine how Bresenham or whomever> could make such a claim to the obvious. Even the DOS writer(s) used> this technique to get one-second time intervals from the 18.206> ticks/per second. This is simply division by subtraction, but you> don't throw away the remainder. Therefore, in the limit, there is> no remainder. However, at any instant, the time can be off by as> much as the divisor -1. FYI, you make digital filters using this> same method, it's hardly novel.It's novel for Linux then, because it seems not to have occured toanyone here.  I'll take your agressive response as a vote in favor.-- Daniel-To unsubscribe from this list: send the line "unsubscribe linux-kernel" inthe body of a message to majordomo@vger.kernel.orgMore majordomo info at  http://vger.kernel.org/majordomo-info.htmlPlease read the FAQ at  http://www.tux.org/lkml/`