Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[mirror_ubuntu-jammy-kernel.git] / Documentation / cgroup-v1 / blkio-controller.txt

diff --git a/Documentation/cgroup-v1/blkio-controller.txt b/Documentation/cgroup-v1/blkio-controller.txt
index 673dc34d3f7812c5030133821e81d9772f8aa546..d1a1b7bdd03add6eb4a0e84b20420ebdaea9dbaf 100644 (file)
--- a/Documentation/cgroup-v1/blkio-controller.txt
+++ b/Documentation/cgroup-v1/blkio-controller.txt
@@ -8,61 +8,13 @@ both at leaf nodes as well as at intermediate nodes in a storage hierarchy.
 Plan is to use the same cgroup based management interface for blkio controller
 and based on user options switch IO policies in the background.
 
 Plan is to use the same cgroup based management interface for blkio controller
 and based on user options switch IO policies in the background.
 

-Currently two IO control policies are implemented. First one is proportional
-weight time based division of disk policy. It is implemented in CFQ. Hence
-this policy takes effect only on leaf nodes when CFQ is being used. The second
-one is throttling policy which can be used to specify upper IO rate limits
-on devices. This policy is implemented in generic block layer and can be
-used on leaf nodes as well as higher level logical devices like device mapper.
+One IO control policy is throttling policy which can be used to
+specify upper IO rate limits on devices. This policy is implemented in
+generic block layer and can be used on leaf nodes as well as higher
+level logical devices like device mapper.

 
 HOWTO
 =====
 
 HOWTO
 =====

-Proportional Weight division of bandwidth
------------------------------------------
-You can do a very simple testing of running two dd threads in two different
-cgroups. Here is what you can do.
-
-- Enable Block IO controller
-       CONFIG_BLK_CGROUP=y
-
-- Enable group scheduling in CFQ
-       CONFIG_CFQ_GROUP_IOSCHED=y
-
-- Compile and boot into kernel and mount IO controller (blkio); see
-  cgroups.txt, Why are cgroups needed?.
-
-       mount -t tmpfs cgroup_root /sys/fs/cgroup
-       mkdir /sys/fs/cgroup/blkio
-       mount -t cgroup -o blkio none /sys/fs/cgroup/blkio
-
-- Create two cgroups
-       mkdir -p /sys/fs/cgroup/blkio/test1/ /sys/fs/cgroup/blkio/test2
-
-- Set weights of group test1 and test2
-       echo 1000 > /sys/fs/cgroup/blkio/test1/blkio.weight
-       echo 500 > /sys/fs/cgroup/blkio/test2/blkio.weight
-
-- Create two same size files (say 512MB each) on same disk (file1, file2) and
-  launch two dd threads in different cgroup to read those files.
-
-       sync
-       echo 3 > /proc/sys/vm/drop_caches
-
-       dd if=/mnt/sdb/zerofile1 of=/dev/null &
-       echo $! > /sys/fs/cgroup/blkio/test1/tasks
-       cat /sys/fs/cgroup/blkio/test1/tasks
-
-       dd if=/mnt/sdb/zerofile2 of=/dev/null &
-       echo $! > /sys/fs/cgroup/blkio/test2/tasks
-       cat /sys/fs/cgroup/blkio/test2/tasks
-
-- At macro level, first dd should finish first. To get more precise data, keep
-  on looking at (with the help of script), at blkio.disk_time and
-  blkio.disk_sectors files of both test1 and test2 groups. This will tell how
-  much disk time (in milliseconds), each group got and how many sectors each
-  group dispatched to the disk. We provide fairness in terms of disk time, so
-  ideally io.disk_time of cgroups should be in proportion to the weight.
-

 Throttling/Upper Limit policy
 -----------------------------
 - Enable Block IO controller
 Throttling/Upper Limit policy
 -----------------------------
 - Enable Block IO controller


@@ -94,7 +46,7 @@ Throttling/Upper Limit policy
 Hierarchical Cgroups
 ====================
 
 Hierarchical Cgroups
 ====================
 

-Both CFQ and throttling implement hierarchy support; however,
+Throttling implements 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.
 throttling's hierarchy support is enabled iff "sane_behavior" is
 enabled from cgroup side, which currently is a development option and
 not publicly available.


@@ -107,9 +59,8 @@ If somebody created a hierarchy like as follows.
                        |
                     test3
 
                        |
                     test3
 

-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
+Throttling with "sane_behavior" will handle the
+hierarchy correctly. For throttling, all limits apply

 to the whole subtree while all statistics are local to the IOs
 directly generated by tasks in that cgroup.
 
 to the whole subtree while all statistics are local to the IOs
 directly generated by tasks in that cgroup.
 


@@ -130,10 +81,6 @@ CONFIG_DEBUG_BLK_CGROUP
        - Debug help. Right now some additional stats file show up in cgroup
          if this option is enabled.
 
        - Debug help. Right now some additional stats file show up in cgroup
          if this option is enabled.
 

-CONFIG_CFQ_GROUP_IOSCHED
-       - Enables group scheduling in CFQ. Currently only 1 level of group
-         creation is allowed.
-

 CONFIG_BLK_DEV_THROTTLING
        - Enable block device throttling support in block layer.
 
 CONFIG_BLK_DEV_THROTTLING
        - Enable block device throttling support in block layer.
 


@@ -344,32 +291,3 @@ Common files among various policies
 - blkio.reset_stats
        - Writing an int to this file will result in resetting all the stats
          for that cgroup.
 - blkio.reset_stats
        - Writing an int to this file will result in resetting all the stats
          for that cgroup.

-
-CFQ sysfs tunable
-=================
-/sys/block/<disk>/queue/iosched/slice_idle
-------------------------------------------
-On a faster hardware CFQ can be slow, especially with sequential workload.
-This happens because CFQ idles on a single queue and single queue might not
-drive deeper request queue depths to keep the storage busy. In such scenarios
-one can try setting slice_idle=0 and that would switch CFQ to IOPS
-(IO operations per second) mode on NCQ supporting hardware.
-
-That means CFQ will not idle between cfq queues of a cfq group and hence be
-able to driver higher queue depth and achieve better throughput. That also
-means that cfq provides fairness among groups in terms of IOPS and not in
-terms of disk time.
-
-/sys/block/<disk>/queue/iosched/group_idle
-------------------------------------------
-If one disables idling on individual cfq queues and cfq service trees by
-setting slice_idle=0, group_idle kicks in. That means CFQ will still idle
-on the group in an attempt to provide fairness among groups.
-
-By default group_idle is same as slice_idle and does not do anything if
-slice_idle is enabled.
-
-One can experience an overall throughput drop if you have created multiple
-groups and put applications in that group which are not driving enough
-IO to keep disk busy. In that case set group_idle=0, and CFQ will not idle
-on individual groups and throughput should improve.