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blk-throttle: implement proper hierarchy support

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With the recent updates, blk-throttle is finally ready for proper
hierarchy support.  Dispatching now honors service_queue->parent_sq
and propagates correctly.  The only thing missing is setting
->parent_sq correctly so that throtl_grp hierarchy matches the cgroup
hierarchy.

This patch updates throtl_pd_init() such that service_queues form the
same hierarchy as the cgroup hierarchy if sane_behavior is enabled.
As this concludes proper hierarchy support for blkcg, the shameful
.broken_hierarchy tag is removed from blkio_subsys.

v2: Updated blkio-controller.txt as suggested by Vivek.

Signed-off-by: Tejun Heo <[email protected]>
Acked-by: Vivek Goyal <[email protected]>
Cc: Li Zefan <[email protected]>
This commit is contained in:
Tejun Heo 2013-05-14 13:52:38 -07:00
commit 9138125bea
4 changed files with 38 additions and 23 deletions
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29
Documentation/cgroups/blkio-controller.txt
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@ -94,11 +94,13 @@ Throttling/Upper Limit policy
Hierarchical Cgroups
====================
- Currently only CFQ supports hierarchical groups. For throttling,
cgroup interface does allow creation of hierarchical cgroups and
internally it treats them as flat hierarchy.
If somebody created a hierarchy like as follows.
Both CFQ and throttling implement hierarchy support; however,
throttling's hierarchy support is enabled iff "sane_behavior" is
enabled from cgroup side, which currently is a development option and
not publicly available.
If somebody created a hierarchy like as follows.
root
/ \
@ -106,21 +108,20 @@ Hierarchical Cgroups
|
test3
CFQ will handle the hierarchy correctly but and throttling will
practically treat all groups at same level. For details on CFQ
hierarchy support, refer to Documentation/block/cfq-iosched.txt.
Throttling will treat the hierarchy as if it looks like the
following.
CFQ by default and throttling with "sane_behavior" will handle the
hierarchy correctly. For details on CFQ hierarchy support, refer to
Documentation/block/cfq-iosched.txt. For throttling, all limits apply
to the whole subtree while all statistics are local to the IOs
directly generated by tasks in that cgroup.
Throttling without "sane_behavior" enabled from cgroup side will
practically treat all groups at same level as if it looks like the
following.
pivot
/ / \ \
root test1 test2 test3
Nesting cgroups, while allowed, isn't officially supported and blkio
genereates warning when cgroups nest. Once throttling implements
hierarchy support, hierarchy will be supported and the warning will
be removed.
Various user visible config options
===================================
CONFIG_BLK_CGROUP