1=======================
2Network priority cgroup
3=======================
4
5The Network priority cgroup provides an interface to allow an administrator to
6dynamically set the priority of network traffic generated by various
7applications
8
9Nominally, an application would set the priority of its traffic via the
10SO_PRIORITY socket option.  This however, is not always possible because:
11
121) The application may not have been coded to set this value
132) The priority of application traffic is often a site-specific administrative
14   decision rather than an application defined one.
15
16This cgroup allows an administrator to assign a process to a group which defines
17the priority of egress traffic on a given interface. Network priority groups can
18be created by first mounting the cgroup filesystem::
19
20	# mount -t cgroup -onet_prio none /sys/fs/cgroup/net_prio
21
22With the above step, the initial group acting as the parent accounting group
23becomes visible at '/sys/fs/cgroup/net_prio'.  This group includes all tasks in
24the system. '/sys/fs/cgroup/net_prio/tasks' lists the tasks in this cgroup.
25
26Each net_prio cgroup contains two files that are subsystem specific
27
28net_prio.prioidx
29  This file is read-only, and is simply informative.  It contains a unique
30  integer value that the kernel uses as an internal representation of this
31  cgroup.
32
33net_prio.ifpriomap
34  This file contains a map of the priorities assigned to traffic originating
35  from processes in this group and egressing the system on various interfaces.
36  It contains a list of tuples in the form <ifname priority>.  Contents of this
37  file can be modified by echoing a string into the file using the same tuple
38  format. For example::
39
40	echo "eth0 5" > /sys/fs/cgroups/net_prio/iscsi/net_prio.ifpriomap
41
42This command would force any traffic originating from processes belonging to the
43iscsi net_prio cgroup and egressing on interface eth0 to have the priority of
44said traffic set to the value 5. The parent accounting group also has a
45writeable 'net_prio.ifpriomap' file that can be used to set a system default
46priority.
47
48Priorities are set immediately prior to queueing a frame to the device
49queueing discipline (qdisc) so priorities will be assigned prior to the hardware
50queue selection being made.
51
52One usage for the net_prio cgroup is with mqprio qdisc allowing application
53traffic to be steered to hardware/driver based traffic classes. These mappings
54can then be managed by administrators or other networking protocols such as
55DCBX.
56
57A new net_prio cgroup inherits the parent's configuration.
58