mirror of https://gitee.com/openkylin/linux.git
79 lines
3.4 KiB
ReStructuredText
79 lines
3.4 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
===========================================
|
|
HOWTO for multiqueue network device support
|
|
===========================================
|
|
|
|
Section 1: Base driver requirements for implementing multiqueue support
|
|
=======================================================================
|
|
|
|
Intro: Kernel support for multiqueue devices
|
|
---------------------------------------------------------
|
|
|
|
Kernel support for multiqueue devices is always present.
|
|
|
|
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.).
|
|
|
|
|
|
Section 2: Qdisc support for multiqueue devices
|
|
===============================================
|
|
|
|
Currently two qdiscs are optimized for 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 head-of-line
|
|
blocking. 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 based on either the simple_tx_hash
|
|
function or based on netdev->select_queue() if you have it defined.
|
|
|
|
The behavior of tc filters remains the same. However a new tc action,
|
|
skbedit, has been added. Assuming you wanted to route all traffic to a
|
|
specific host, for example 192.168.0.3, through a specific queue you could use
|
|
this action and establish a filter such as::
|
|
|
|
tc filter add dev eth0 parent 1: protocol ip prio 1 u32 \
|
|
match ip dst 192.168.0.3 \
|
|
action skbedit queue_mapping 3
|
|
|
|
:Author: Alexander Duyck <alexander.h.duyck@intel.com>
|
|
:Original Author: Peter P. Waskiewicz Jr. <peter.p.waskiewicz.jr@intel.com>
|