lkml.org 
[lkml]   [2002]   [Jul]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: HZ, preferably as small as possible
    Date
    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.

    --
    Daniel
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 13:27    [W:0.022 / U:1.272 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site