q_cake: Add description of the tc filter override mechanism to man page

Since CAKE now has three different settings that can be overridden by tc
filters (priority and host and flow hashes), documenting how they work is
probably a good idea.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

diff --git a/man/man8/tc-cake.8 b/man/man8/tc-cake.8
index c1e751d68d8d6c9a86d981e17fa1e393454d4a88..c62e55475d0d0fdcf15e49ad69dba3ed25fe5d5b 100644 (file)
--- a/man/man8/tc-cake.8
+++ b/man/man8/tc-cake.8
@@ -569,6 +569,61 @@ possible latency. At link speeds higher than 10 Gbps, setting the
 no-split-gso parameter can increase the maximum achievable throughput by
 retaining the full GSO packets.
 
+.SH OVERRIDING CLASSIFICATION WITH TC FILTERS
+
+CAKE supports overriding of its internal classification of packets through the
+tc filter mechanism. Packets can be assigned to different priority tins by
+setting the
+.B priority
+field on the skb, and the flow hashing can be overridden by setting the
+.B classid
+parameter.
+
+.PP
+.B Tin override
+
+.br
+        To assign a priority tin, the major number of the priority field needs
+to match the qdisc handle of the cake instance; if it does, the minor number
+will be interpreted as the tin index. For example, to classify all ICMP packets
+as 'bulk', the following filter can be used:
+
+.br
+        # tc qdisc replace dev eth0 handle 1: root cake diffserv3
+        # tc filter add dev eth0 parent 1: protocol ip prio 1 \\
+          u32 match icmp type 0 0 action skbedit priority 1:1
+
+.PP
+.B Flow hash override
+
+.br
+        To override flow hashing, the classid can be set. CAKE will interpret
+the major number of the classid as the host hash used in host isolation mode,
+and the minor number as the flow hash used for flow-based queueing. One or both
+of those can be set, and will be used if the relevant flow isolation parameter
+is set (i.e., the major number will be ignored if CAKE is not configured in
+hosts mode, and the minor number will be ignored if CAKE is not configured in
+flows mode).
+
+.br
+This example will assign all ICMP packets to the first queue:
+
+.br
+        # tc qdisc replace dev eth0 handle 1: root cake
+        # tc filter add dev eth0 parent 1: protocol ip prio 1 \\
+          u32 match icmp type 0 0 classid 0:1
+
+.br
+If only one of the host and flow overrides is set, CAKE will compute the other
+hash from the packet as normal. Note, however, that the host isolation mode
+works by assigning a host ID to the flow queue; so if overriding both host and
+flow, the same flow cannot have more than one host assigned. In addition, it is
+not possible to assign different source and destination host IDs through the
+override mechanism; if a host ID is assigned, it will be used as both source and
+destination host.
+
+
+
 .SH EXAMPLES
 # tc qdisc delete root dev eth0
 .br