netdev - [PATCH v2 iproute2-next] sch_cake: Make gso-splitting configurable

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Message-Id: <20180813113617.13073-1-toke@toke.dk>
Date:   Mon, 13 Aug 2018 13:36:17 +0200
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     David Ahern <dsahern@...il.com>
Cc:     netdev@...r.kernel.org,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        Dave Taht <dave.taht@...il.com>
Subject: [PATCH v2 iproute2-next] sch_cake: Make gso-splitting configurable

This patch makes sch_cake's gso/gro splitting configurable
from userspace.

To disable breaking apart superpackets in sch_cake:

tc qdisc replace dev whatever root cake no-split-gso

to enable:

tc qdisc replace dev whatever root cake split-gso

Signed-off-by: Toke Høiland-Jørgensen <toke@...e.dk>
Signed-off-by: Dave Taht <dave.taht@...il.com>
---
v2:
  - Fix x-mas tree variable order
  - Also update man page

 man/man8/tc-cake.8 | 23 +++++++++++++++++++++++
 tc/q_cake.c        |  9 +++++++++
 2 files changed, 32 insertions(+)

diff --git a/man/man8/tc-cake.8 b/man/man8/tc-cake.8
index 0e84bc6e..b8e3089b 100644
--- a/man/man8/tc-cake.8
+++ b/man/man8/tc-cake.8
@@ -73,6 +73,12 @@ TIME |
 ]
 .br
 [
+.BR split-gso*
+|
+.BR no-split-gso
+]
+.br
+[
 .BR ack-filter
 |
 .BR ack-filter-aggressive
@@ -546,6 +552,23 @@ If you are shaping inbound, and cannot trust the diffserv markings (as is the
 case for Comcast Cable, among others), it is best to use a single queue
 "besteffort" mode with wash.
 
+.PP
+.B split-gso
+
+.br
+	This option controls whether CAKE will split General Segmentation
+Offload (GSO) super-packets into their on-the-wire components and
+dequeue them individually.
+
+.br
+Super-packets are created by the networking stack to improve efficiency.
+However, because they are larger they take longer to dequeue, which
+translates to higher latency for competing flows, especially at lower
+bandwidths. CAKE defaults to splitting GSO packets to achieve the lowest
+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 EXAMPLES
 # tc qdisc delete root dev eth0
 .br
diff --git a/tc/q_cake.c b/tc/q_cake.c
index f1e232a6..50de46a7 100644
--- a/tc/q_cake.c
+++ b/tc/q_cake.c
@@ -79,6 +79,7 @@ static void explain(void)
 "                  dual-srchost | dual-dsthost | triple-isolate* ]\n"
 "                [ nat | nonat* ]\n"
 "                [ wash | nowash* ]\n"
+"                [ split-gso* | no-split-gso ]\n"
 "                [ ack-filter | ack-filter-aggressive | no-ack-filter* ]\n"
 "                [ memlimit LIMIT ]\n"
 "                [ ptm | atm | noatm* ] [ overhead N | conservative | raw* ]\n"
@@ -99,6 +100,7 @@ static int cake_parse_opt(struct qdisc_util *qu, int argc, char **argv,
 	__u64 bandwidth = 0;
 	int ack_filter = -1;
 	struct rtattr *tail;
+	int split_gso = -1;
 	int unlimited = 0;
 	int flowmode = -1;
 	int autorate = -1;
@@ -155,6 +157,10 @@ static int cake_parse_opt(struct qdisc_util *qu, int argc, char **argv,
 			wash = 0;
 		} else if (strcmp(*argv, "wash") == 0) {
 			wash = 1;
+		} else if (strcmp(*argv, "split-gso") == 0) {
+			split_gso = 1;
+		} else if (strcmp(*argv, "no-split-gso") == 0) {
+			split_gso = 0;
 		} else if (strcmp(*argv, "flowblind") == 0) {
 			flowmode = CAKE_FLOW_NONE;
 		} else if (strcmp(*argv, "srchost") == 0) {
@@ -374,6 +380,9 @@ static int cake_parse_opt(struct qdisc_util *qu, int argc, char **argv,
 		addattr_l(n, 1024, TCA_CAKE_NAT, &nat, sizeof(nat));
 	if (wash != -1)
 		addattr_l(n, 1024, TCA_CAKE_WASH, &wash, sizeof(wash));
+	if (split_gso != -1)
+		addattr_l(n, 1024, TCA_CAKE_SPLIT_GSO, &split_gso,
+			  sizeof(split_gso));
 	if (ingress != -1)
 		addattr_l(n, 1024, TCA_CAKE_INGRESS, &ingress, sizeof(ingress));
 	if (ack_filter != -1)
-- 
2.18.0