58 lines
2.5 KiB
ReStructuredText
58 lines
2.5 KiB
ReStructuredText
=======================
|
|
Network priority cgroup
|
|
=======================
|
|
|
|
The Network priority cgroup provides an interface to allow an administrator to
|
|
dynamically set the priority of network traffic generated by various
|
|
applications
|
|
|
|
Nominally, an application would set the priority of its traffic via the
|
|
SO_PRIORITY socket option. This however, is not always possible because:
|
|
|
|
1) The application may not have been coded to set this value
|
|
2) The priority of application traffic is often a site-specific administrative
|
|
decision rather than an application defined one.
|
|
|
|
This cgroup allows an administrator to assign a process to a group which defines
|
|
the priority of egress traffic on a given interface. Network priority groups can
|
|
be created by first mounting the cgroup filesystem::
|
|
|
|
# mount -t cgroup -onet_prio none /sys/fs/cgroup/net_prio
|
|
|
|
With the above step, the initial group acting as the parent accounting group
|
|
becomes visible at '/sys/fs/cgroup/net_prio'. This group includes all tasks in
|
|
the system. '/sys/fs/cgroup/net_prio/tasks' lists the tasks in this cgroup.
|
|
|
|
Each net_prio cgroup contains two files that are subsystem specific
|
|
|
|
net_prio.prioidx
|
|
This file is read-only, and is simply informative. It contains a unique
|
|
integer value that the kernel uses as an internal representation of this
|
|
cgroup.
|
|
|
|
net_prio.ifpriomap
|
|
This file contains a map of the priorities assigned to traffic originating
|
|
from processes in this group and egressing the system on various interfaces.
|
|
It contains a list of tuples in the form <ifname priority>. Contents of this
|
|
file can be modified by echoing a string into the file using the same tuple
|
|
format. For example::
|
|
|
|
echo "eth0 5" > /sys/fs/cgroups/net_prio/iscsi/net_prio.ifpriomap
|
|
|
|
This command would force any traffic originating from processes belonging to the
|
|
iscsi net_prio cgroup and egressing on interface eth0 to have the priority of
|
|
said traffic set to the value 5. The parent accounting group also has a
|
|
writeable 'net_prio.ifpriomap' file that can be used to set a system default
|
|
priority.
|
|
|
|
Priorities are set immediately prior to queueing a frame to the device
|
|
queueing discipline (qdisc) so priorities will be assigned prior to the hardware
|
|
queue selection being made.
|
|
|
|
One usage for the net_prio cgroup is with mqprio qdisc allowing application
|
|
traffic to be steered to hardware/driver based traffic classes. These mappings
|
|
can then be managed by administrators or other networking protocols such as
|
|
DCBX.
|
|
|
|
A new net_prio cgroup inherits the parent's configuration.
|