Messages in this thread | | | From | Daniel Phillips <> | Subject | Re: HZ, preferably as small as possible | Date | Wed, 17 Jul 2002 21:33:07 +0200 |
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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.
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