[PATCH iproute2-next] tc: red: allow setting th_min and th_max to the same value

[Jakub Kicinski]

Setting th_min and th_max to the same value may be useful for DCTCP
deployments.  The original DCTCP paper describes it as a simplest way
of achieving simple ECN threshold marking.  Indeed, there doesn't seem
to be any simpler qdisc in Linux which would allow such a setup today.

Signed-off-by: Jakub Kicinski <jakub.kicin...@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vanderme...@netronome.com>
---
Or should I go ahead and add a DCTCP qdisc? :)

 tc/tc_red.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tc/tc_red.c b/tc/tc_red.c
index 1f82ef1aec65..178fe088f732 100644
--- a/tc/tc_red.c
+++ b/tc/tc_red.c
@@ -30,7 +30,9 @@ int tc_red_eval_P(unsigned int qmin, unsigned int qmax, 
double prob)
 {
        int i = qmax - qmin;
 
-       if (i <= 0)
+       if (!i)
+               return 0;
+       if (i < 0)
                return -1;
 
        prob /= i;
-- 
2.15.1