Commit | Line | Data |
---|---|---|
a093bf00 PWJ |
1 | |
2 | HOWTO for multiqueue network device support | |
3 | =========================================== | |
4 | ||
5 | Section 1: Base driver requirements for implementing multiqueue support | |
a093bf00 PWJ |
6 | |
7 | Intro: Kernel support for multiqueue devices | |
8 | --------------------------------------------------------- | |
9 | ||
b19fa1fa | 10 | Kernel support for multiqueue devices is always present. |
a093bf00 PWJ |
11 | |
12 | Section 1: Base driver requirements for implementing multiqueue support | |
13 | ----------------------------------------------------------------------- | |
14 | ||
15 | Base drivers are required to use the new alloc_etherdev_mq() or | |
16 | alloc_netdev_mq() functions to allocate the subqueues for the device. The | |
17 | underlying kernel API will take care of the allocation and deallocation of | |
18 | the subqueue memory, as well as netdev configuration of where the queues | |
19 | exist in memory. | |
20 | ||
21 | The base driver will also need to manage the queues as it does the global | |
22 | netdev->queue_lock today. Therefore base drivers should use the | |
23 | netif_{start|stop|wake}_subqueue() functions to manage each queue while the | |
24 | device is still operational. netdev->queue_lock is still used when the device | |
25 | comes online or when it's completely shut down (unregister_netdev(), etc.). | |
26 | ||
92651940 AD |
27 | |
28 | Section 2: Qdisc support for multiqueue devices | |
29 | ||
30 | ----------------------------------------------- | |
31 | ||
f07d1501 AD |
32 | Currently two qdiscs are optimized for multiqueue devices. The first is the |
33 | default pfifo_fast qdisc. This qdisc supports one qdisc per hardware queue. | |
34 | A new round-robin qdisc, sch_multiq also supports multiple hardware queues. The | |
92651940 AD |
35 | qdisc is responsible for classifying the skb's and then directing the skb's to |
36 | bands and queues based on the value in skb->queue_mapping. Use this field in | |
37 | the base driver to determine which queue to send the skb to. | |
38 | ||
f07d1501 AD |
39 | sch_multiq has been added for hardware that wishes to avoid head-of-line |
40 | blocking. It will cycle though the bands and verify that the hardware queue | |
92651940 AD |
41 | associated with the band is not stopped prior to dequeuing a packet. |
42 | ||
43 | On qdisc load, the number of bands is based on the number of queues on the | |
44 | hardware. Once the association is made, any skb with skb->queue_mapping set, | |
45 | will be queued to the band associated with the hardware queue. | |
46 | ||
47 | ||
48 | Section 3: Brief howto using MULTIQ for multiqueue devices | |
49 | --------------------------------------------------------------- | |
50 | ||
51 | The userspace command 'tc,' part of the iproute2 package, is used to configure | |
52 | qdiscs. To add the MULTIQ qdisc to your network device, assuming the device | |
53 | is called eth0, run the following command: | |
54 | ||
55 | # tc qdisc add dev eth0 root handle 1: multiq | |
56 | ||
57 | The qdisc will allocate the number of bands to equal the number of queues that | |
58 | the device reports, and bring the qdisc online. Assuming eth0 has 4 Tx | |
59 | queues, the band mapping would look like: | |
60 | ||
61 | band 0 => queue 0 | |
62 | band 1 => queue 1 | |
63 | band 2 => queue 2 | |
64 | band 3 => queue 3 | |
65 | ||
f07d1501 AD |
66 | Traffic will begin flowing through each queue based on either the simple_tx_hash |
67 | function or based on netdev->select_queue() if you have it defined. | |
92651940 | 68 | |
ca9b0e27 AD |
69 | The behavior of tc filters remains the same. However a new tc action, |
70 | skbedit, has been added. Assuming you wanted to route all traffic to a | |
67333bb5 | 71 | specific host, for example 192.168.0.3, through a specific queue you could use |
ca9b0e27 AD |
72 | this action and establish a filter such as: |
73 | ||
74 | tc filter add dev eth0 parent 1: protocol ip prio 1 u32 \ | |
75 | match ip dst 192.168.0.3 \ | |
76 | action skbedit queue_mapping 3 | |
92651940 AD |
77 | |
78 | Author: Alexander Duyck <alexander.h.duyck@intel.com> | |
79 | Original Author: Peter P. Waskiewicz Jr. <peter.p.waskiewicz.jr@intel.com> |