lkml.org 
[lkml]   [2010]   [Jun]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] ppp_generic: fix multilink fragment sizes
    Paoloni, Gabriele wrote:
    > The proposed patch looks wrong to me.
    >
    > nbigger is already doing the job; I didn't use DIV_ROUND_UP because in general we don't have always to roundup, otherwise we would exceed the total bandwidth.

    I was basing this on the original code prior to your patch, which used
    DIV_ROUND_UP to get the fragment size. Looking more closely I see your
    point, the original code was starting with the larger fragment size and
    decrementing rather than starting with the smaller size and incrementing
    as your code does, so that makes sense.


    >
    > flen = len;
    > if (nfree > 0) {
    > if (pch->speed == 0) {
    > - flen = totlen/nfree;
    > + if (nfree > 1)
    > + flen = DIV_ROUND_UP(len, nfree);
    > if (nbigger > 0) {
    > flen++;
    > nbigger--;

    The important change here is the use of 'len' instead of 'totlen'.
    'nfree' and 'len' should decrease roughly proportionally with each
    iteration of the loop whereas 'totlen' remains unchanged. Thus
    (totlen/nfree) gets bigger on each iteration whereas len/nfree should
    give roughly the same. However, without rounding up here I'm not sure
    the logic is right either, since the side effect of nbigger is to make
    len decrease faster so it is not quite proportional to the decrease in
    nfree. Is there a risk of ending up on the nfree == 1 iteration with
    flen == len - 1 and thus generating a superfluous extra 1 byte long
    fragment? This would be a far worse situation than a slight imbalance
    in the size of the fragments.

    Perhaps the solution is to go back to a precalculated fragment size for
    the pch->speed == 0 case as per original code?

    Regards,
    Ben.


    \
     
     \ /
      Last update: 2010-06-02 17:59    [W:0.025 / U:0.248 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site