Re: [PATCH net v3 1/7] net/sched: netem: fix probability gaps in 4-state loss model

Simon Horman
2026-04-04T09:50:04Z

On Thu, Apr 02, 2026 at 01:19:29PM -0700, Stephen Hemminger wrote:
> The 4-state Markov chain in loss_4state() has gaps at the boundaries
> between transition probability ranges. The comparisons use:
>
> if (rnd < a4)
> else if (a4 < rnd && rnd < a1 + a4)
>
> When rnd equals a boundary value exactly, neither branch matches and
> no state transition occurs. The redundant lower-bound check (a4 < rnd)
> is already implied by being in the else branch.
>
> Remove the unnecessary lower-bound comparisons so the ranges are
> contiguous and every random value produces a transition, matching
> the GI (General and Intuitive) loss model specification.
>
> This bug goes back to original implementation of this model.
>
> Fixes: 661b79725fea ("netem: revised correlated loss generator")
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

Reviewed-by: Simon Horman <horms@kernel.org>