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authorNeil Horman <nhorman@tuxdriver.com>2011-11-22 05:10:52 +0000
committerDavid S. Miller <davem@davemloft.net>2011-11-22 15:22:23 -0500
commit3ee32fee65ef6a4a8a4188e913be7dd90ba9e058 (patch)
tree5d450d446498258decc755f65c77c9140102a132 /Documentation/cgroups/net_prio.txt
parent5bc1421e34ecfe0bd4b26dc3232b7d5e25179144 (diff)
net: add documentation for net_prio cgroups (v4)
Add the requisite documentation to explain to new users how net_prio cgroups work Signed-off-by:Neil Horman <nhorman@tuxdriver.com> Signed-off-by: John Fastabend <john.r.fastabend@intel.com> CC: Robert Love <robert.w.love@intel.com> CC: "David S. Miller" <davem@davemloft.net> Signed-off-by: David S. Miller <davem@davemloft.net>
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+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.