[PATCH 2/2] Documentation: describe burst reset on quota changes

[Zhe Liu]

Document that an incompatible burst is reset when a finite quota is
written through the cgroup v1 or cgroup v2 CPU bandwidth interface, while
compatible bursts and unlimited quota updates preserve the existing value.

Signed-off-by: Zhe Liu <liuzhe1@xxxxxxxxxx>
---
 Documentation/admin-guide/cgroup-v2.rst |  5 ++++-
 Documentation/scheduler/sched-bwc.rst   | 14 ++++++++------
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index aed195a71cbf..9f5e43d96476 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1200,7 +1200,10 @@ will be referred to. All time durations are in microseconds.
 
 	which indicates that the group may consume up to $MAX in each
 	$PERIOD duration.  "max" for $MAX indicates no limit.  If only
-	one number is written, $MAX is updated.
+	one number is written, $MAX is updated.  When a finite $MAX is
+	written, an existing cpu.max.burst value which is incompatible
+	with the new limit is reset to zero.  Writing "max" leaves the
+	burst value unchanged.
 
 	This file affects only processes under the fair-class scheduler.
 
diff --git a/Documentation/scheduler/sched-bwc.rst b/Documentation/scheduler/sched-bwc.rst
index e881a945c188..79bd5f254e50 100644
--- a/Documentation/scheduler/sched-bwc.rst
+++ b/Documentation/scheduler/sched-bwc.rst
@@ -90,14 +90,16 @@ bandwidth restriction in place, such a group is described as an unconstrained
 bandwidth group. This represents the traditional work-conserving behavior for
 CFS.
 
-Writing any (valid) positive value(s) no smaller than cpu.cfs_burst_us will
-enact the specified bandwidth limit. The minimum quota allowed for the quota or
-period is 1ms. There is also an upper bound on the period length of 1s.
-Additional restrictions exist when bandwidth limits are used in a hierarchical
-fashion, these are explained in more detail below.
+Writing any valid positive value will enact the specified bandwidth limit. If
+the existing cpu.cfs_burst_us value is incompatible with the new quota, it is
+reset to zero. The minimum quota allowed for the quota or period is 1ms. There
+is also an upper bound on the period length of 1s. Additional restrictions
+exist when bandwidth limits are used in a hierarchical fashion, these are
+explained in more detail below.
 
 Writing any negative value to cpu.cfs_quota_us will remove the bandwidth limit
-and return the group to an unconstrained state once more.
+and return the group to an unconstrained state once more. The existing
+cpu.cfs_burst_us value remains unchanged.
 
 A value of 0 for cpu.cfs_burst_us indicates that the group can not accumulate
 any unused bandwidth. It makes the traditional bandwidth control behavior for
-- 
2.25.1