Add a brief howto to Documentation/networking for multiqueue. It
explains how to use the multiqueue API in a driver to support
multiqueue paths from the stack, as well as the qdiscs to use for
feeding a multiqueue device.
Signed-off-by: Peter P Waskiewicz Jr <[EMAIL PROTECTED]>
---
Documentation/networking/multiqueue.txt | 98 +++++++++++++++++++++++++++++++
1 files changed, 98 insertions(+), 0 deletions(-)
diff --git a/Documentation/networking/multiqueue.txt
b/Documentation/networking/multiqueue.txt
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+
+ HOWTO for multiqueue network device support
+ ===========================================
+
+Section 1: Base driver requirements for implementing multiqueue support
+Section 2: Qdisc support for multiqueue devices
+Section 3: Brief howto using PRIO for multiqueue devices
+
+
+Intro: Kernel support for multiqueue devices
+---------------------------------------------------------
+
+Kernel support for multiqueue devices is only an API that is presented to the
+netdevice layer for base drivers to implement. This feature is part of the
+core networking stack, and all network devices will be running on the
+multiqueue-aware stack. If a base driver only has one queue, then these
+changes are transparent to that driver.
+
+
+Section 2: Base driver requirements for implementing multiqueue support
+-----------------------------------------------------------------------
+
+Base drivers are required to use the new alloc_etherdev_mq() or
+alloc_netdev_mq() functions to allocate the subqueues for the device. The
+underlying kernel API will take care of the allocation and deallocation of
+the subqueue memory, as well as netdev configuration of where the queues
+exist in memory.
+
+The base driver will also need to manage the queues as it does the global
+netdev->queue_lock today. Therefore base drivers should use the
+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.).
+
+Finally, the base driver should indicate that it is a multiqueue device. The
+feature flag NETIF_F_MULTI_QUEUE should be added to the netdev->features
+bitmap on device initialization. Below is an example from e1000:
+
+#ifdef CONFIG_E1000_MQ
+ if ( (adapter->hw.mac.type == e1000_82571) ||
+ (adapter->hw.mac.type == e1000_82572) ||
+ (adapter->hw.mac.type == e1000_80003es2lan))
+ netdev->features |= NETIF_F_MULTI_QUEUE;
+#endif
+
+
+Section 3: Qdisc support for multiqueue devices
+-----------------------------------------------
+
+Currently two qdiscs support multiqueue devices. A new round-robin qdisc,
+sch_rr, and sch_prio. The qdisc is responsible for classifying the skb's to
+bands and queues, and will store the queue mapping into skb->queue_mapping.
+Use this field in the base driver to determine which queue to send the skb
+to.
+
+sch_rr has been added for hardware that doesn't want scheduling policies from
+software, so it's a straight round-robin qdisc. It uses the same syntax and
+classification priomap that sch_prio uses, so it should be intuitive to
+configure for people who've used sch_prio.
+
+The PRIO qdisc naturally plugs into a multiqueue device. Upon load of the
+qdisc, PRIO will make a best-effort assignment of queue to PRIO band to evenly
+distribute traffic flows. The algorithm can be found in prio_tune() in
+net/sched/sch_prio.c. Once the association is made, any skb that is
+classified will have skb->queue_mapping set, which will allow the driver to
+properly queue skb's to multiple queues. sch_prio can have these features
+compiled in or out of the module.
+
+
+Section 4: Brief howto using PRIO for multiqueue devices
+--------------------------------------------------------
+
+The userspace command 'tc,' part of the iproute2 package, is used to configure
+qdiscs. To add the PRIO qdisc to your network device, assuming the device is
+called eth0, run the following command:
+
+# tc qdisc add dev eth0 root handle 1: prio
+
+This will create 3 bands, 0 being highest priority, and associate those bands
+to the queues on your NIC. Assuming eth0 has 2 Tx queues, the band mapping
+would look like:
+
+band 0 => queue 0
+band 1 => queue 1
+band 2 => queue 1
+
+Traffic will begin flowing through each queue if your TOS values are assigning
+traffic across the various bands. For example, ssh traffic will always try to
+go out band 0 based on TOS -> Linux priority conversion (realtime traffic),
+so it will be sent out queue 0. ICMP traffic (pings) fall into the "normal"
+traffic classification, which is band 1. Therefore pings will be send out
+queue 1 on the NIC.
+
+The behavior of tc filters remains the same, where it will override TOS
priority
+classification.
+
+
+Author: Peter P. Waskiewicz Jr. <[EMAIL PROTECTED]>
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