netdev - [PATCH] net: make tc-police action MTU behavior match documentation

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Date:   Mon, 26 Feb 2018 13:10:15 -0700
From:   Andrew Collins <acollins@...dlepoint.com>
To:     jhs@...atatu.com, xiyou.wangcong@...il.com, davem@...emloft.net,
        netdev@...r.kernel.org
Cc:     Andrew Collins <acollins@...dlepoint.com>
Subject: [PATCH] net: make tc-police action MTU behavior match documentation

The man page for tc-police states that the MTU defaults to
unlimited if peakrate is not specified, but it actually defaults
to 2047.

This causes issues with GRO enabled interfaces, as >2047 coalesced
packets get dropped and the resulting rate is wildly inaccurate.

Fix by only setting the default MTU when peakrate is specified.

Longer term act_police should likely segment GRO packets like
sch_tbf does, but I see no clear way to accomplish this within
a tc action.

Signed-off-by: Andrew Collins <acollins@...dlepoint.com>
---
 net/sched/act_police.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/act_police.c b/net/sched/act_police.c
index 95d3c9097b25..36b8c92f644c 100644
--- a/net/sched/act_police.c
+++ b/net/sched/act_police.c
@@ -149,7 +149,7 @@ static int tcf_act_police_init(struct net *net, struct nlattr *nla,
 	police->tcfp_mtu = parm->mtu;
 	if (police->tcfp_mtu == 0) {
 		police->tcfp_mtu = ~0;
-		if (R_tab)
+		if (R_tab && P_tab)
 			police->tcfp_mtu = 255 << R_tab->rate.cell_log;
 	}
 	if (R_tab) {
-- 
2.14.3