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