sched: Implement interface for cgroup unified hierarchy

There are a couple interface issues which can be addressed in cgroup2
interface.

* Stats from cpuacct being reported separately from the cpu stats.

* Use of different time units.  Writable control knobs use
  microseconds, some stat fields use nanoseconds while other cpuacct
  stat fields use centiseconds.

* Control knobs which can't be used in the root cgroup still show up
  in the root.

* Control knob names and semantics aren't consistent with other
  controllers.

This patchset implements cpu controller's interface on cgroup2 which
adheres to the controller file conventions described in
Documentation/cgroups/cgroup-v2.txt.  Overall, the following changes
are made.

* cpuacct is implictly enabled and disabled by cpu and its information
  is reported through "cpu.stat" which now uses microseconds for all
  time durations.  All time duration fields now have "_usec" appended
  to them for clarity.

  Note that cpuacct.usage_percpu is currently not included in
  "cpu.stat".  If this information is actually called for, it will be
  added later.

* "cpu.shares" is replaced with "cpu.weight" and operates on the
  standard scale defined by CGROUP_WEIGHT_MIN/DFL/MAX (1, 100, 10000).
  The weight is scaled to scheduler weight so that 100 maps to 1024
  and the ratio relationship is preserved - if weight is W and its
  scaled value is S, W / 100 == S / 1024.  While the mapped range is a
  bit smaller than the orignal scheduler weight range, the dead zones
  on both sides are relatively small and covers wider range than the
  nice value mappings.  This file doesn't make sense in the root
  cgroup and isn't created on root.

* "cpu.weight.nice" is added. When read, it reads back the nice value
  which is closest to the current "cpu.weight".  When written, it sets
  "cpu.weight" to the weight value which matches the nice value.  This
  makes it easy to configure cgroups when they're competing against
  threads in threaded subtrees.

* "cpu.cfs_quota_us" and "cpu.cfs_period_us" are replaced by "cpu.max"
  which contains both quota and period.

v4: - Use cgroup2 basic usage stat as the information source instead
      of cpuacct.

v3: - Added "cpu.weight.nice" to allow using nice values when
      configuring the weight.  The feature is requested by PeterZ.
    - Merge the patch to enable threaded support on cpu and cpuacct.
    - Dropped the bits about getting rid of cpuacct from patch
      description as there is a pretty strong case for making cpuacct
      an implicit controller so that basic cpu usage stats are always
      available.
    - Documentation updated accordingly.  "cpu.rt.max" section is
      dropped for now.

v2: - cpu_stats_show() was incorrectly using CONFIG_FAIR_GROUP_SCHED
      for CFS bandwidth stats and also using raw division for u64.
      Use CONFIG_CFS_BANDWITH and do_div() instead.  "cpu.rt.max" is
      not included yet.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>

1 files changed, 12 insertions, 24 deletions

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 3f8216912df0..0bbdc720dd7c 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -902,10 +902,6 @@ Controllers
 CPU
 ---
 
-.. note::
-
-	The interface for the cpu controller hasn't been merged yet
-
 The "cpu" controllers regulates distribution of CPU cycles.  This
 controller implements weight and absolute bandwidth limit models for
 normal scheduling policy and absolute bandwidth allocation model for
@@ -935,6 +931,18 @@ All time durations are in microseconds.
 
 	The weight in the range [1, 10000].
 
+  cpu.weight.nice
+	A read-write single value file which exists on non-root
+	cgroups.  The default is "0".
+
+	The nice value is in the range [-20, 19].
+
+	This interface file is an alternative interface for
+	"cpu.weight" and allows reading and setting weight using the
+	same values used by nice(2).  Because the range is smaller and
+	granularity is coarser for the nice values, the read value is
+	the closest approximation of the current weight.
+
   cpu.max
 	A read-write two value file which exists on non-root cgroups.
 	The default is "max 100000".
@@ -947,26 +955,6 @@ All time durations are in microseconds.
 	$PERIOD duration.  "max" for $MAX indicates no limit.  If only
 	one number is written, $MAX is updated.
 
-  cpu.rt.max
-	.. note::
-
-	   The semantics of this file is still under discussion and the
-	   interface hasn't been merged yet
-
-	A read-write two value file which exists on all cgroups.
-	The default is "0 100000".
-
-	The maximum realtime runtime allocation.  Over-committing
-	configurations are disallowed and process migrations are
-	rejected if not enough bandwidth is available.  It's in the
-	following format::
-
-	  $MAX $PERIOD
-
-	which indicates that the group may consume upto $MAX in each
-	$PERIOD duration.  If only one number is written, $MAX is
-	updated.
-
 
 Memory
 ------