pkt_sched: Add multiqueue scheduler support

This patch is intended to add a qdisc to support the new tx multiqueue
architecture by providing a band for each hardware queue.  By doing
this it is possible to support a different qdisc per physical hardware
queue.

This qdisc uses the skb->queue_mapping to select which band to place
the traffic onto.  It then uses a round robin w/ a check to see if the
subqueue is stopped to determine which band to dequeue the packet from.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/multiqueue.txt

@@ -24,4 +24,49 @@ netif_{start|stop|wake}_subqueue() functions to manage each queue while the
 device is still operational.  netdev->queue_lock is still used when the device
 comes online or when it's completely shut down (unregister_netdev(), etc.).
 
-Author: Peter P. Waskiewicz Jr. <peter.p.waskiewicz.jr@intel.com>
+
+Section 2: Qdisc support for multiqueue devices
+
+-----------------------------------------------
+
+Currently two qdiscs support multiqueue devices.  The first is the default
+pfifo_fast qdisc.  This qdisc supports one qdisc per hardware queue.  A new
+round-robin qdisc, sch_multiq also supports multiple hardware queues. The
+qdisc is responsible for classifying the skb's and then directing the skb's to
+bands and queues based on the value in skb->queue_mapping.  Use this field in
+the base driver to determine which queue to send the skb to.
+
+sch_multiq has been added for hardware that wishes to avoid unnecessary
+requeuing.  It will cycle though the bands and verify that the hardware queue
+associated with the band is not stopped prior to dequeuing a packet.
+
+On qdisc load, the number of bands is based on the number of queues on the
+hardware.  Once the association is made, any skb with skb->queue_mapping set,
+will be queued to the band associated with the hardware queue.
+
+
+Section 3: Brief howto using MULTIQ for multiqueue devices
+---------------------------------------------------------------
+
+The userspace command 'tc,' part of the iproute2 package, is used to configure
+qdiscs.  To add the MULTIQ qdisc to your network device, assuming the device
+is called eth0, run the following command:
+
+# tc qdisc add dev eth0 root handle 1: multiq
+
+The qdisc will allocate the number of bands to equal the number of queues that
+the device reports, and bring the qdisc online.  Assuming eth0 has 4 Tx
+queues, the band mapping would look like:
+
+band 0 => queue 0
+band 1 => queue 1
+band 2 => queue 2
+band 3 => queue 3
+
+Traffic will begin flowing through each queue if your base device has either
+the default simple_tx_hash or a custom netdev->select_queue() defined.
+
+The behavior of tc filters remains the same.
+
+Author: Alexander Duyck <alexander.h.duyck@intel.com>
+Original Author: Peter P. Waskiewicz Jr. <peter.p.waskiewicz.jr@intel.com>

include/linux/pkt_sched.h

@@ -123,6 +123,13 @@ struct tc_prio_qopt
 	__u8	priomap[TC_PRIO_MAX+1];	/* Map: logical priority -> PRIO band */
 };
 
+/* MULTIQ section */
+
+struct tc_multiq_qopt {
+	__u16	bands;			/* Number of bands */
+	__u16	max_bands;		/* Maximum number of queues */
+};
+
 /* TBF section */
 
 struct tc_tbf_qopt

net/sched/Kconfig

@@ -106,6 +106,15 @@ config NET_SCH_PRIO
 	  To compile this code as a module, choose M here: the
 	  module will be called sch_prio.
 
+config NET_SCH_MULTIQ
+	tristate "Hardware Multiqueue-aware Multi Band Queuing (MULTIQ)"
+	---help---
+	  Say Y here if you want to use an n-band queue packet scheduler
+	  to support devices that have multiple hardware transmit queues.
+
+	  To compile this code as a module, choose M here: the
+	  module will be called sch_multiq.
+
 config NET_SCH_RED
 	tristate "Random Early Detection (RED)"
 	---help---

net/sched/Makefile

@@ -26,6 +26,7 @@ obj-$(CONFIG_NET_SCH_SFQ)	+= sch_sfq.o
 obj-$(CONFIG_NET_SCH_TBF)	+= sch_tbf.o
 obj-$(CONFIG_NET_SCH_TEQL)	+= sch_teql.o
 obj-$(CONFIG_NET_SCH_PRIO)	+= sch_prio.o
+obj-$(CONFIG_NET_SCH_MULTIQ)	+= sch_multiq.o
 obj-$(CONFIG_NET_SCH_ATM)	+= sch_atm.o
 obj-$(CONFIG_NET_SCH_NETEM)	+= sch_netem.o
 obj-$(CONFIG_NET_CLS_U32)	+= cls_u32.o