[PATCH net-next v1 3/3] sch_cake: Simplify logic in cake_select_tin()

[Toke Høiland-Jørgensen]

From: Toke Høiland-Jørgensen <t...@toke.dk>

With more modes added the logic in cake_select_tin() was getting a bit
hairy, and it turns out we can actually simplify it quite a bit. This also
allows us to get rid of one of the two diffserv parsing functions, which
has the added benefit that already-zeroed DSCP fields won't get re-written.

Suggested-by: Kevin Darbyshire-Bryant <l...@darbyshire-bryant.me.uk>
Signed-off-by: Toke Høiland-Jørgensen <t...@redhat.com>
---
 net/sched/sch_cake.c |   61 +++++++++++++++++++-------------------------------
 1 file changed, 23 insertions(+), 38 deletions(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index f1cc4779699b..1d2a12132abc 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1513,20 +1513,6 @@ static unsigned int cake_drop(struct Qdisc *sch, struct 
sk_buff **to_free)
        return idx + (tin << 16);
 }
 
-static void cake_wash_diffserv(struct sk_buff *skb)
-{
-       switch (skb->protocol) {
-       case htons(ETH_P_IP):
-               ipv4_change_dsfield(ip_hdr(skb), INET_ECN_MASK, 0);
-               break;
-       case htons(ETH_P_IPV6):
-               ipv6_change_dsfield(ipv6_hdr(skb), INET_ECN_MASK, 0);
-               break;
-       default:
-               break;
-       }
-}
-
 static u8 cake_handle_diffserv(struct sk_buff *skb, u16 wash)
 {
        u8 dscp;
@@ -1558,33 +1544,32 @@ static struct cake_tin_data *cake_select_tin(struct 
Qdisc *sch,
 {
        struct cake_sched_data *q = qdisc_priv(sch);
        u32 tin;
+       u8 dscp;
 
-       if (TC_H_MAJ(skb->priority) == sch->handle &&
-           TC_H_MIN(skb->priority) > 0 &&
-           TC_H_MIN(skb->priority) <= q->tin_cnt) {
-               tin = q->tin_order[TC_H_MIN(skb->priority) - 1];
+       /* Tin selection: Default to diffserv-based selection, allow overriding
+        * using firewall marks or skb->priority.
+        */
+       dscp = cake_handle_diffserv(skb,
+                                   q->rate_flags & CAKE_FLAG_WASH);
 
-               if (q->rate_flags & CAKE_FLAG_WASH)
-                       cake_wash_diffserv(skb);
-       } else if (q->tin_mode != CAKE_DIFFSERV_BESTEFFORT) {
-               if (q->rate_flags & CAKE_FLAG_FWMARK && /* use fw mark */
-                   skb->mark &&
-                   skb->mark <= q->tin_cnt) {
-                       tin = q->tin_order[skb->mark - 1];
-                       if (q->rate_flags & CAKE_FLAG_WASH)
-                               cake_wash_diffserv(skb);
-               } else {
-                       /* extract the Diffserv Precedence field, if it exists 
*/
-                       /* and clear DSCP bits if washing */
-                       tin = q->tin_index[cake_handle_diffserv(skb,
-                                       q->rate_flags & CAKE_FLAG_WASH)];
-                       if (unlikely(tin >= q->tin_cnt))
-                               tin = 0;
-               }
-       } else {
+       if (q->tin_mode == CAKE_DIFFSERV_BESTEFFORT)
                tin = 0;
-               if (q->rate_flags & CAKE_FLAG_WASH)
-                       cake_wash_diffserv(skb);
+
+       else if (q->rate_flags & CAKE_FLAG_FWMARK && /* use fw mark */
+                skb->mark &&
+                skb->mark <= q->tin_cnt)
+               tin = q->tin_order[skb->mark - 1];
+
+       else if (TC_H_MAJ(skb->priority) == sch->handle &&
+                TC_H_MIN(skb->priority) > 0 &&
+                TC_H_MIN(skb->priority) <= q->tin_cnt)
+               tin = q->tin_order[TC_H_MIN(skb->priority) - 1];
+
+       else {
+               tin = q->tin_index[dscp];
+
+               if (unlikely(tin >= q->tin_cnt))
+                       tin = 0;
        }
 
        return &q->tins[tin];