netdev - [PATCH iproute2-next] tc: red: allow setting th_min and th

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Message-Id: <20180116230850.25802-1-jakub.kicinski@netronome.com>
Date:   Tue, 16 Jan 2018 15:08:50 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     dsahern@...il.com, stephen@...workplumber.org
Cc:     netdev@...r.kernel.org, oss-drivers@...ronome.com,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: [PATCH iproute2-next] tc: red: allow setting th_min and th_max to the same value

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.kicinski@...ronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@...ronome.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