• Ilpo Järvinen's avatar
    [PKT_SCHED] RED: Fix overflow in calculation of queue average · c4c0ce5c
    Ilpo Järvinen authored
    Overflow can occur very easily with 32 bits, e.g., with 1 second
    us_idle is approx. 2^20, which leaves only 11-Wlog bits for queue
    length. Since the EWMA exponent is typically around 9, queue
    lengths larger than 2^2 cause overflow. Whether the affected
    branch is taken when us_idle is as high as 1 second, depends on
    Scell_log, but with rather reasonable configuration Scell_log is
    large enough to cause p->Stab to have zero index, which always
    results zero shift (typically also few other small indices result
    in zero shift).
    Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>