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3 | =========================================== |
4 | HOWTO for multiqueue network device support | |
5 | =========================================== | |
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6 | |
7 | Section 1: Base driver requirements for implementing multiqueue support | |
e98aa682 | 8 | ======================================================================= |
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9 | |
10 | Intro: Kernel support for multiqueue devices | |
11 | --------------------------------------------------------- | |
12 | ||
b19fa1fa | 13 | Kernel support for multiqueue devices is always present. |
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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 | ||
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27 | |
28 | Section 2: Qdisc support for multiqueue devices | |
e98aa682 | 29 | =============================================== |
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31 | Currently two qdiscs are optimized for multiqueue devices. The first is the |
32 | default pfifo_fast qdisc. This qdisc supports one qdisc per hardware queue. | |
33 | A new round-robin qdisc, sch_multiq also supports multiple hardware queues. The | |
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34 | qdisc is responsible for classifying the skb's and then directing the skb's to |
35 | bands and queues based on the value in skb->queue_mapping. Use this field in | |
36 | the base driver to determine which queue to send the skb to. | |
37 | ||
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38 | sch_multiq has been added for hardware that wishes to avoid head-of-line |
39 | blocking. It will cycle though the bands and verify that the hardware queue | |
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40 | associated with the band is not stopped prior to dequeuing a packet. |
41 | ||
42 | On qdisc load, the number of bands is based on the number of queues on the | |
43 | hardware. Once the association is made, any skb with skb->queue_mapping set, | |
44 | will be queued to the band associated with the hardware queue. | |
45 | ||
46 | ||
47 | Section 3: Brief howto using MULTIQ for multiqueue devices | |
e98aa682 | 48 | ========================================================== |
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49 | |
50 | The userspace command 'tc,' part of the iproute2 package, is used to configure | |
51 | qdiscs. To add the MULTIQ qdisc to your network device, assuming the device | |
e98aa682 | 52 | is called eth0, run the following command:: |
92651940 | 53 | |
e98aa682 | 54 | # tc qdisc add dev eth0 root handle 1: multiq |
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55 | |
56 | The qdisc will allocate the number of bands to equal the number of queues that | |
57 | the device reports, and bring the qdisc online. Assuming eth0 has 4 Tx | |
e98aa682 | 58 | queues, the band mapping would look like:: |
92651940 | 59 | |
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60 | band 0 => queue 0 |
61 | band 1 => queue 1 | |
62 | band 2 => queue 2 | |
63 | band 3 => queue 3 | |
92651940 | 64 | |
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65 | Traffic will begin flowing through each queue based on either the simple_tx_hash |
66 | function or based on netdev->select_queue() if you have it defined. | |
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68 | The behavior of tc filters remains the same. However a new tc action, |
69 | skbedit, has been added. Assuming you wanted to route all traffic to a | |
67333bb5 | 70 | specific host, for example 192.168.0.3, through a specific queue you could use |
e98aa682 | 71 | this action and establish a filter such as:: |
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73 | tc filter add dev eth0 parent 1: protocol ip prio 1 u32 \ |
74 | match ip dst 192.168.0.3 \ | |
75 | action skbedit queue_mapping 3 | |
92651940 | 76 | |
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77 | :Author: Alexander Duyck <alexander.h.duyck@intel.com> |
78 | :Original Author: Peter P. Waskiewicz Jr. <peter.p.waskiewicz.jr@intel.com> |