net: pkt_sched: PIE AQM scheme

Proportional Integral controller Enhanced (PIE) is a scheduler to address the
bufferbloat problem.

>From the IETF draft below:
" Bufferbloat is a phenomenon where excess buffers in the network cause high
latency and jitter. As more and more interactive applications (e.g. voice over
IP, real time video streaming and financial transactions) run in the Internet,
high latency and jitter degrade application performance. There is a pressing
need to design intelligent queue management schemes that can control latency and
jitter; and hence provide desirable quality of service to users.

We present here a lightweight design, PIE(Proportional Integral controller
Enhanced) that can effectively control the average queueing latency to a target
value. Simulation results, theoretical analysis and Linux testbed results have
shown that PIE can ensure low latency and achieve high link utilization under
various congestion situations. The design does not require per-packet
timestamp, so it incurs very small overhead and is simple enough to implement
in both hardware and software.  "

Many thanks to Dave Taht for extensive feedback, reviews, testing and
suggestions. Thanks also to Stephen Hemminger and Eric Dumazet for reviews and
suggestions.  Naeem Khademi and Dave Taht independently contributed to ECN
support.

For more information, please see technical paper about PIE in the IEEE
Conference on High Performance Switching and Routing 2013. A copy of the paper
can be found at ftp://ftpeng.cisco.com/pie/.

Please also refer to the IETF draft submission at
http://tools.ietf.org/html/draft-pan-tsvwg-pie-00

All relevant code, documents and test scripts and results can be found at
ftp://ftpeng.cisco.com/pie/.

For problems with the iproute2/tc or Linux kernel code, please contact Vijay
Subramanian (vijaynsu@cisco.com or subramanian.vijay@gmail.com) Mythili Prabhu
(mysuryan@cisco.com)

Signed-off-by: Vijay Subramanian <subramanian.vijay@gmail.com>
Signed-off-by: Mythili Prabhu <mysuryan@cisco.com>
CC: Dave Taht <dave.taht@bufferbloat.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/pkt_sched.h

@@ -818,4 +818,29 @@ struct tc_hhf_xstats {
 	__u32	hh_tot_count;   /* number of captured heavy-hitters so far */
 	__u32	hh_cur_count;   /* number of current heavy-hitters */
 };
+
+/* PIE */
+enum {
+	TCA_PIE_UNSPEC,
+	TCA_PIE_TARGET,
+	TCA_PIE_LIMIT,
+	TCA_PIE_TUPDATE,
+	TCA_PIE_ALPHA,
+	TCA_PIE_BETA,
+	TCA_PIE_ECN,
+	TCA_PIE_BYTEMODE,
+	__TCA_PIE_MAX
+};
+#define TCA_PIE_MAX   (__TCA_PIE_MAX - 1)
+
+struct tc_pie_xstats {
+	__u32 prob;             /* current probability */
+	__u32 delay;            /* current delay in ms */
+	__u32 avg_dq_rate;      /* current average dq_rate in bits/pie_time */
+	__u32 packets_in;       /* total number of packets enqueued */
+	__u32 dropped;          /* packets dropped due to pie_action */
+	__u32 overlimit;        /* dropped due to lack of space in queue */
+	__u32 maxq;             /* maximum queue size */
+	__u32 ecn_mark;         /* packets marked with ecn*/
+};
 #endif

net/sched/Kconfig

@@ -295,6 +295,19 @@ config NET_SCH_HHF
 	  To compile this driver as a module, choose M here: the module
 	  will be called sch_hhf.
 
+config NET_SCH_PIE
+	tristate "Proportional Integral controller Enhanced (PIE) scheduler"
+	help
+	  Say Y here if you want to use the Proportional Integral controller
+	  Enhanced scheduler packet scheduling algorithm.
+	  For more information, please see
+	  http://tools.ietf.org/html/draft-pan-tsvwg-pie-00
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called sch_pie.
+
+	  If unsure, say N.
+
 config NET_SCH_INGRESS
 	tristate "Ingress Qdisc"
 	depends on NET_CLS_ACT

net/sched/Makefile

@@ -41,6 +41,7 @@ obj-$(CONFIG_NET_SCH_CODEL)	+= sch_codel.o
 obj-$(CONFIG_NET_SCH_FQ_CODEL)	+= sch_fq_codel.o
 obj-$(CONFIG_NET_SCH_FQ)	+= sch_fq.o
 obj-$(CONFIG_NET_SCH_HHF)	+= sch_hhf.o
+obj-$(CONFIG_NET_SCH_PIE)	+= sch_pie.o
 
 obj-$(CONFIG_NET_CLS_U32)	+= cls_u32.o
 obj-$(CONFIG_NET_CLS_ROUTE4)	+= cls_route.o