Document the independent quota and burst configuration and the runtime burst clamp.
Signed-off-by: Zhe Liu <[email protected]> --- Documentation/admin-guide/cgroup-v2.rst | 5 ++++- Documentation/scheduler/sched-bwc.rst | 21 ++++++++++++--------- 2 files changed, 16 insertions(+), 10 deletions(-) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 7c2a8ed80071..57253c2c1819 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1229,7 +1229,10 @@ will be referred to. All time durations are in microseconds. A read-write single value file which exists on non-root cgroups. The default is "0". - The burst in the range [0, $MAX]. + The burst in the range [0, $MAX]. The configured value is retained when + the quota changes and may be larger than the current quota. During CFS + runtime refill, the effective burst is limited to the current quota. + The quota and burst files can therefore be written in either order. 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..08a54ee84da2 100644 --- a/Documentation/scheduler/sched-bwc.rst +++ b/Documentation/scheduler/sched-bwc.rst @@ -90,20 +90,22 @@ 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 quota value 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 negative value to cpu.cfs_quota_us will remove the bandwidth limit and return the group to an unconstrained state once more. 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 -CFS unchanged. Writing any (valid) positive value(s) no larger than -cpu.cfs_quota_us into cpu.cfs_burst_us will enact the cap on unused bandwidth -accumulation. +CFS unchanged. A valid positive value written to cpu.cfs_burst_us is retained +when the quota changes. If it is larger than the current quota, CFS limits the +effective burst during runtime refill to the current quota. + +The quota and burst files can be updated in either order. Any updates to a group's bandwidth specification will result in it becoming unthrottled if it is in a constrained state. @@ -243,4 +245,5 @@ Examples # echo 50000 > cpu.cfs_period_us /* period = 50ms */ # echo 10000 > cpu.cfs_burst_us /* burst = 10ms */ - Larger buffer setting (no larger than quota) allows greater burst capacity. + A larger buffer setting allows greater burst capacity. If the configured + burst is larger than the quota, the effective burst is limited to the quota. -- 2.25.1
