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Subject[PATCH 8/8] blkio-cgroup: Document for blkio.use_hierarchy.
Document for blkio.use_hierarchy.

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
---
Documentation/cgroups/blkio-controller.txt | 58 +++++++++++++++++++---------
1 files changed, 39 insertions(+), 19 deletions(-)
diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
index 4ed7b5c..9c6dc9e 100644
--- a/Documentation/cgroups/blkio-controller.txt
+++ b/Documentation/cgroups/blkio-controller.txt
@@ -91,30 +91,44 @@ Throttling/Upper Limit policy

Hierarchical Cgroups
====================
-- Currently none of the IO control policy supports hierarhical groups. But
- cgroup interface does allow creation of hierarhical cgroups and internally
- IO policies treat them as flat hierarchy.
+- Cgroup interface allows creation of hierarchical cgroups. Currently,
+ internally IO policies are able to treat them as flat hierarchy or
+ hierarchical hierarchy. Both hierarchical bandwidth division and flat
+ bandwidth division are supported. "blkio.use_hierarchy" can be used to
+ switch between flat mode and hierarchical mode.

- So this patch will allow creation of cgroup hierarhcy but at the backend
- everything will be treated as flat. So if somebody created a hierarchy like
- as follows.
+ Consider the following CGroup hierarchy:

- root
- / \
- test1 test2
- |
- test3
+ Root
+ / | \
+ Grp1 Grp2 tsk1
+ / \
+ Grp3 tsk2

- CFQ and throttling will practically treat all groups at same level.
+ If flat mode is enabled, CFQ and throttling will practically treat all
+ groups at the same level.

- pivot
- / | \ \
- root test1 test2 test3
+ Pivot tree
+ / | | \
+ Root Grp1 Grp2 Grp3
+ / |
+ tsk1 tsk2

- Down the line we can implement hierarchical accounting/control support
- and also introduce a new cgroup file "use_hierarchy" which will control
- whether cgroup hierarchy is viewed as flat or hierarchical by the policy..
- This is how memory controller also has implemented the things.
+ If hierarchical mode is enabled, CFQ will treat groups and tasks as the same
+ view in CGroup hierarchy.
+
+ Root
+ / | \
+ Grp1 Grp2 tsk1
+ / \
+ Grp3 tsk2
+
+ Grp1, Grp2 and tsk1 are treated at the same level under Root group. Grp3 and
+ tsk2 are treated at the same level under Grp1. Below is the mapping between
+ task io priority and io weight:
+
+ prio 0 1 2 3 4 5 6 7
+ weight 1000 868 740 612 484 356 228 100

Various user visible config options
===================================
@@ -169,6 +183,12 @@ Proportional weight policy files
dev weight
8:16 300

+- blkio.use_hierarchy
+ - Switch between hierarchical mode and flat mode as stated above.
+ blkio.use_hierarchy == 1 means hierarchical mode is enabled.
+ blkio.use_hierarchy == 0 means flat mode is enabled.
+ The default mode is flat mode.
+
- blkio.time
- disk time allocated to cgroup per device in milliseconds. First
two fields specify the major and minor number of the device and
--
1.6.5.2



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