Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 375 insertions, 0 deletions

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+				Block IO Controller
+				===================
+Overview
+========
+cgroup subsys "blkio" implements the block io controller. There seems to be
+a need of various kinds of IO control policies (like proportional BW, max BW)
+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.
+
+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.
+
+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
+	CONFIG_BLK_CGROUP=y
+
+- Enable throttling in block layer
+	CONFIG_BLK_DEV_THROTTLING=y
+
+- Mount blkio controller (see cgroups.txt, Why are cgroups needed?)
+        mount -t cgroup -o blkio none /sys/fs/cgroup/blkio
+
+- Specify a bandwidth rate on particular device for root group. The format
+  for policy is "<major>:<minor>  <bytes_per_second>".
+
+        echo "8:16  1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
+
+  Above will put a limit of 1MB/second on reads happening for root group
+  on device having major/minor number 8:16.
+
+- Run dd to read a file and see if rate is throttled to 1MB/s or not.
+
+        # dd iflag=direct if=/mnt/common/zerofile of=/dev/null bs=4K count=1024
+        1024+0 records in
+        1024+0 records out
+        4194304 bytes (4.2 MB) copied, 4.0001 s, 1.0 MB/s
+
+ Limits for writes can be put using blkio.throttle.write_bps_device file.
+
+Hierarchical Cgroups
+====================
+
+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
+			/  \
+		     test1 test2
+			|
+		     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
+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
+
+Various user visible config options
+===================================
+CONFIG_BLK_CGROUP
+	- Block IO controller.
+
+CONFIG_DEBUG_BLK_CGROUP
+	- 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.
+
+Details of cgroup files
+=======================
+Proportional weight policy files
+--------------------------------
+- blkio.weight
+	- Specifies per cgroup weight. This is default weight of the group
+	  on all the devices until and unless overridden by per device rule.
+	  (See blkio.weight_device).
+	  Currently allowed range of weights is from 10 to 1000.
+
+- blkio.weight_device
+	- One can specify per cgroup per device rules using this interface.
+	  These rules override the default value of group weight as specified
+	  by blkio.weight.
+
+	  Following is the format.
+
+	  # echo dev_maj:dev_minor weight > blkio.weight_device
+	  Configure weight=300 on /dev/sdb (8:16) in this cgroup
+	  # echo 8:16 300 > blkio.weight_device
+	  # cat blkio.weight_device
+	  dev     weight
+	  8:16    300
+
+	  Configure weight=500 on /dev/sda (8:0) in this cgroup
+	  # echo 8:0 500 > blkio.weight_device
+	  # cat blkio.weight_device
+	  dev     weight
+	  8:0     500
+	  8:16    300
+
+	  Remove specific weight for /dev/sda in this cgroup
+	  # echo 8:0 0 > blkio.weight_device
+	  # cat blkio.weight_device
+	  dev     weight
+	  8:16    300
+
+- blkio.leaf_weight[_device]
+	- Equivalents of blkio.weight[_device] for the purpose of
+          deciding how much weight tasks in the given cgroup has while
+          competing with the cgroup's child cgroups. For details,
+          please refer to Documentation/block/cfq-iosched.txt.
+
+- blkio.time
+	- disk time allocated to cgroup per device in milliseconds. First
+	  two fields specify the major and minor number of the device and
+	  third field specifies the disk time allocated to group in
+	  milliseconds.
+
+- blkio.sectors
+	- number of sectors transferred to/from disk by the group. First
+	  two fields specify the major and minor number of the device and
+	  third field specifies the number of sectors transferred by the
+	  group to/from the device.
+
+- blkio.io_service_bytes
+	- Number of bytes transferred to/from the disk by the group. These
+	  are further divided by the type of operation - read or write, sync
+	  or async. First two fields specify the major and minor number of the
+	  device, third field specifies the operation type and the fourth field
+	  specifies the number of bytes.
+
+- blkio.io_serviced
+	- Number of IOs (bio) issued to the disk by the group. These
+	  are further divided by the type of operation - read or write, sync
+	  or async. First two fields specify the major and minor number of the
+	  device, third field specifies the operation type and the fourth field
+	  specifies the number of IOs.
+
+- blkio.io_service_time
+	- Total amount of time between request dispatch and request completion
+	  for the IOs done by this cgroup. This is in nanoseconds to make it
+	  meaningful for flash devices too. For devices with queue depth of 1,
+	  this time represents the actual service time. When queue_depth > 1,
+	  that is no longer true as requests may be served out of order. This
+	  may cause the service time for a given IO to include the service time
+	  of multiple IOs when served out of order which may result in total
+	  io_service_time > actual time elapsed. This time is further divided by
+	  the type of operation - read or write, sync or async. First two fields
+	  specify the major and minor number of the device, third field
+	  specifies the operation type and the fourth field specifies the
+	  io_service_time in ns.
+
+- blkio.io_wait_time
+	- Total amount of time the IOs for this cgroup spent waiting in the
+	  scheduler queues for service. This can be greater than the total time
+	  elapsed since it is cumulative io_wait_time for all IOs. It is not a
+	  measure of total time the cgroup spent waiting but rather a measure of
+	  the wait_time for its individual IOs. For devices with queue_depth > 1
+	  this metric does not include the time spent waiting for service once
+	  the IO is dispatched to the device but till it actually gets serviced
+	  (there might be a time lag here due to re-ordering of requests by the
+	  device). This is in nanoseconds to make it meaningful for flash
+	  devices too. This time is further divided by the type of operation -
+	  read or write, sync or async. First two fields specify the major and
+	  minor number of the device, third field specifies the operation type
+	  and the fourth field specifies the io_wait_time in ns.
+
+- blkio.io_merged
+	- Total number of bios/requests merged into requests belonging to this
+	  cgroup. This is further divided by the type of operation - read or
+	  write, sync or async.
+
+- blkio.io_queued
+	- Total number of requests queued up at any given instant for this
+	  cgroup. This is further divided by the type of operation - read or
+	  write, sync or async.
+
+- blkio.avg_queue_size
+	- Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y.
+	  The average queue size for this cgroup over the entire time of this
+	  cgroup's existence. Queue size samples are taken each time one of the
+	  queues of this cgroup gets a timeslice.
+
+- blkio.group_wait_time
+	- Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y.
+	  This is the amount of time the cgroup had to wait since it became busy
+	  (i.e., went from 0 to 1 request queued) to get a timeslice for one of
+	  its queues. This is different from the io_wait_time which is the
+	  cumulative total of the amount of time spent by each IO in that cgroup
+	  waiting in the scheduler queue. This is in nanoseconds. If this is
+	  read when the cgroup is in a waiting (for timeslice) state, the stat
+	  will only report the group_wait_time accumulated till the last time it
+	  got a timeslice and will not include the current delta.
+
+- blkio.empty_time
+	- Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y.
+	  This is the amount of time a cgroup spends without any pending
+	  requests when not being served, i.e., it does not include any time
+	  spent idling for one of the queues of the cgroup. This is in
+	  nanoseconds. If this is read when the cgroup is in an empty state,
+	  the stat will only report the empty_time accumulated till the last
+	  time it had a pending request and will not include the current delta.
+
+- blkio.idle_time
+	- Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y.
+	  This is the amount of time spent by the IO scheduler idling for a
+	  given cgroup in anticipation of a better request than the existing ones
+	  from other queues/cgroups. This is in nanoseconds. If this is read
+	  when the cgroup is in an idling state, the stat will only report the
+	  idle_time accumulated till the last idle period and will not include
+	  the current delta.
+
+- blkio.dequeue
+	- Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y. This
+	  gives the statistics about how many a times a group was dequeued
+	  from service tree of the device. First two fields specify the major
+	  and minor number of the device and third field specifies the number
+	  of times a group was dequeued from a particular device.
+
+- blkio.*_recursive
+	- Recursive version of various stats. These files show the
+          same information as their non-recursive counterparts but
+          include stats from all the descendant cgroups.
+
+Throttling/Upper limit policy files
+-----------------------------------
+- blkio.throttle.read_bps_device
+	- Specifies upper limit on READ rate from the device. IO rate is
+	  specified in bytes per second. Rules are per device. Following is
+	  the format.
+
+  echo "<major>:<minor>  <rate_bytes_per_second>" > /cgrp/blkio.throttle.read_bps_device
+
+- blkio.throttle.write_bps_device
+	- Specifies upper limit on WRITE rate to the device. IO rate is
+	  specified in bytes per second. Rules are per device. Following is
+	  the format.
+
+  echo "<major>:<minor>  <rate_bytes_per_second>" > /cgrp/blkio.throttle.write_bps_device
+
+- blkio.throttle.read_iops_device
+	- Specifies upper limit on READ rate from the device. IO rate is
+	  specified in IO per second. Rules are per device. Following is
+	  the format.
+
+  echo "<major>:<minor>  <rate_io_per_second>" > /cgrp/blkio.throttle.read_iops_device
+
+- blkio.throttle.write_iops_device
+	- Specifies upper limit on WRITE rate to the device. IO rate is
+	  specified in io per second. Rules are per device. Following is
+	  the format.
+
+  echo "<major>:<minor>  <rate_io_per_second>" > /cgrp/blkio.throttle.write_iops_device
+
+Note: If both BW and IOPS rules are specified for a device, then IO is
+      subjected to both the constraints.
+
+- blkio.throttle.io_serviced
+	- Number of IOs (bio) issued to the disk by the group. These
+	  are further divided by the type of operation - read or write, sync
+	  or async. First two fields specify the major and minor number of the
+	  device, third field specifies the operation type and the fourth field
+	  specifies the number of IOs.
+
+- blkio.throttle.io_service_bytes
+	- Number of bytes transferred to/from the disk by the group. These
+	  are further divided by the type of operation - read or write, sync
+	  or async. First two fields specify the major and minor number of the
+	  device, third field specifies the operation type and the fourth field
+	  specifies the number of bytes.
+
+Common files among various policies
+-----------------------------------
+- 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.