[2/2] net: add documentation for net_prio cgroups (v2)

Submitted by Neil Horman on Nov. 17, 2011, 9:47 p.m.


Message ID 1321566472-28969-3-git-send-email-nhorman@tuxdriver.com
State Superseded
Delegated to: David Miller
Headers show

Commit Message

Neil Horman Nov. 17, 2011, 9:47 p.m.
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>
 Documentation/cgroups/net_prio.txt |   53 ++++++++++++++++++++++++++++++++++++
 1 files changed, 53 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/cgroups/net_prio.txt

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diff --git a/Documentation/cgroups/net_prio.txt b/Documentation/cgroups/net_prio.txt
new file mode 100644
index 0000000..01b3226
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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
+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
+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.
+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
+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