Merge branch 'for-3.9/core' of git://git.kernel.dk/linux-block

Pull block IO core bits from Jens Axboe:
 "Below are the core block IO bits for 3.9.  It was delayed a few days
  since my workstation kept crashing every 2-8h after pulling it into
  current -git, but turns out it is a bug in the new pstate code (divide
  by zero, will report separately).  In any case, it contains:

   - The big cfq/blkcg update from Tejun and and Vivek.

   - Additional block and writeback tracepoints from Tejun.

   - Improvement of the should sort (based on queues) logic in the plug
     flushing.

   - _io() variants of the wait_for_completion() interface, using
     io_schedule() instead of schedule() to contribute to io wait
     properly.

   - Various little fixes.

  You'll get two trivial merge conflicts, which should be easy enough to
  fix up"

Fix up the trivial conflicts due to hlist traversal cleanups (commit
b67bfe0: "hlist: drop the node parameter from iterators").

* 'for-3.9/core' of git://git.kernel.dk/linux-block: (39 commits)
  block: remove redundant check to bd_openers()
  block: use i_size_write() in bd_set_size()
  cfq: fix lock imbalance with failed allocations
  drivers/block/swim3.c: fix null pointer dereference
  block: don't select PERCPU_RWSEM
  block: account iowait time when waiting for completion of IO request
  sched: add wait_for_completion_io[_timeout]
  writeback: add more tracepoints
  block: add block_{touch|dirty}_buffer tracepoint
  buffer: make touch_buffer() an exported function
  block: add @Req to bio_{front|back}_merge tracepoints
  block: add missing block_bio_complete() tracepoint
  block: Remove should_sort judgement when flush blk_plug
  block,elevator: use new hashtable implementation
  cfq-iosched: add hierarchical cfq_group statistics
  cfq-iosched: collect stats from dead cfqgs
  cfq-iosched: separate out cfqg_stats_reset() from cfq_pd_reset_stats()
  blkcg: make blkcg_print_blkgs() grab q locks instead of blkcg lock
  block: RCU free request_queue
  blkcg: implement blkg_[rw]stat_recursive_sum() and blkg_[rw]stat_merge()
  ...

Documentation/block/cfq-iosched.txt

@@ -102,6 +102,64 @@ processing of request. Therefore, increasing the value can imporve the
 performace although this can cause the latency of some I/O to increase due
 to more number of requests.
 
+CFQ Group scheduling
+====================
+
+CFQ supports blkio cgroup and has "blkio." prefixed files in each
+blkio cgroup directory. It is weight-based and there are four knobs
+for configuration - weight[_device] and leaf_weight[_device].
+Internal cgroup nodes (the ones with children) can also have tasks in
+them, so the former two configure how much proportion the cgroup as a
+whole is entitled to at its parent's level while the latter two
+configure how much proportion the tasks in the cgroup have compared to
+its direct children.
+
+Another way to think about it is assuming that each internal node has
+an implicit leaf child node which hosts all the tasks whose weight is
+configured by leaf_weight[_device]. Let's assume a blkio hierarchy
+composed of five cgroups - root, A, B, AA and AB - with the following
+weights where the names represent the hierarchy.
+
+        weight leaf_weight
+ root :  125    125
+ A    :  500    750
+ B    :  250    500
+ AA   :  500    500
+ AB   : 1000    500
+
+root never has a parent making its weight is meaningless. For backward
+compatibility, weight is always kept in sync with leaf_weight. B, AA
+and AB have no child and thus its tasks have no children cgroup to
+compete with. They always get 100% of what the cgroup won at the
+parent level. Considering only the weights which matter, the hierarchy
+looks like the following.
+
+          root
+       /    |   \
+      A     B    leaf
+     500   250   125
+   /  |  \
+  AA  AB  leaf
+ 500 1000 750
+
+If all cgroups have active IOs and competing with each other, disk
+time will be distributed like the following.
+
+Distribution below root. The total active weight at this level is
+A:500 + B:250 + C:125 = 875.
+
+ root-leaf :   125 /  875      =~ 14%
+ A         :   500 /  875      =~ 57%
+ B(-leaf)  :   250 /  875      =~ 28%
+
+A has children and further distributes its 57% among the children and
+the implicit leaf node. The total active weight at this level is
+AA:500 + AB:1000 + A-leaf:750 = 2250.
+
+ A-leaf    : ( 750 / 2250) * A =~ 19%
+ AA(-leaf) : ( 500 / 2250) * A =~ 12%
+ AB(-leaf) : (1000 / 2250) * A =~ 25%
+
 CFQ IOPS Mode for group scheduling
 ===================================
 Basic CFQ design is to provide priority based time slices. Higher priority

Documentation/cgroups/blkio-controller.txt

@@ -94,30 +94,32 @@ Throttling/Upper Limit policy
 
 Hierarchical Cgroups
 ====================
-- Currently none of the IO control policy supports hierarchical groups. But
-  cgroup interface does allow creation of hierarchical cgroups and internally
-  IO policies treat them as flat hierarchy.
+- Currently only CFQ supports hierarchical groups. For throttling,
+  cgroup interface does allow creation of hierarchical cgroups and
+  internally it treats them as flat hierarchy.
 
-  So this patch will allow creation of cgroup hierarchcy but at the backend
-  everything will be treated as flat. So if somebody created a hierarchy like
-  as follows.
+  If somebody created a hierarchy like as follows.
 
 			root
 			/  \
 		     test1 test2
 			|
 		     test3
 
-  CFQ and throttling will practically treat all groups at same level.
+  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.
 
 				pivot
 			     /  /   \  \
 			root  test1 test2  test3
 
-  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.
+  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
 ===================================
@@ -172,6 +174,12 @@ Proportional weight policy files
 	  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
@@ -279,6 +287,11 @@ Proportional weight policy files
 	  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

block/Kconfig

@@ -4,7 +4,6 @@
 menuconfig BLOCK
        bool "Enable the block layer" if EXPERT
        default y
-       select PERCPU_RWSEM
        help
 	 Provide block layer support for the kernel.