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Documentation / cgroups / net_prio.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:00 EST.

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