1Network priority cgroup
2-------------------------
3
4The Network priority cgroup provides an interface to allow an administrator to
5dynamically set the priority of network traffic generated by various
6applications
7
8Nominally, an application would set the priority of its traffic via the
9SO_PRIORITY socket option.  This however, is not always possible because:
10
111) The application may not have been coded to set this value
122) The priority of application traffic is often a site-specific administrative
13   decision rather than an application defined one.
14
15This cgroup allows an administrator to assign a process to a group which defines
16the priority of egress traffic on a given interface. Network priority groups can
17be created by first mounting the cgroup filesystem.
18
19# mount -t cgroup -onet_prio none /sys/fs/cgroup/net_prio
20
21With the above step, the initial group acting as the parent accounting group
22becomes visible at '/sys/fs/cgroup/net_prio'.  This group includes all tasks in
23the system. '/sys/fs/cgroup/net_prio/tasks' lists the tasks in this cgroup.
24
25Each net_prio cgroup contains two files that are subsystem specific
26
27net_prio.prioidx
28This file is read-only, and is simply informative.  It contains a unique integer
29value that the kernel uses as an internal representation of this cgroup.
30
31net_prio.ifpriomap
32This file contains a map of the priorities assigned to traffic originating from
33processes in this group and egressing the system on various interfaces. It
34contains a list of tuples in the form <ifname priority>.  Contents of this file
35can be modified by echoing a string into the file using the same tuple format.
36for example:
37
38echo "eth0 5" > /sys/fs/cgroups/net_prio/iscsi/net_prio.ifpriomap
39
40This command would force any traffic originating from processes belonging to the
41iscsi net_prio cgroup and egressing on interface eth0 to have the priority of
42said traffic set to the value 5. The parent accounting group also has a
43writeable 'net_prio.ifpriomap' file that can be used to set a system default
44priority.
45
46Priorities are set immediately prior to queueing a frame to the device
47queueing discipline (qdisc) so priorities will be assigned prior to the hardware
48queue selection being made.
49
50One usage for the net_prio cgroup is with mqprio qdisc allowing application
51traffic to be steered to hardware/driver based traffic classes. These mappings
52can then be managed by administrators or other networking protocols such as
53DCBX.
54
55A new net_prio cgroup inherits the parent's configuration.
56