Based on kernel version 3.9. Page generated on 2013-05-02 22:55 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.