Documentation/scheduler/sched-bwc.rst

2 CFS Bandwidth Control
5 [ This document only discusses CPU bandwidth control for SCHED_NORMAL.
6   The SCHED_RT case is covered in Documentation/scheduler/sched-rt-group.rst ]
8 CFS bandwidth control is a CONFIG_FAIR_GROUP_SCHED extension which allows the
13 microseconds of CPU time. That quota is assigned to per-cpu run queues in
16 throttled. Throttled threads will not be able to run again until the next
21 is transferred to cpu-local "silos" on a demand basis. The amount transferred
25 ----------
28 cpu.cfs_quota_us: the total available run-time within a period (in microseconds)
35 	cpu.cfs_quota=-1
37 A value of -1 for cpu.cfs_quota_us indicates that the group does not have any
39 bandwidth group. This represents the traditional work-conserving behavior for
55 --------------------
56 For efficiency run-time is transferred between the global pool and CPU local
66 for more fine-grained consumption.
69 ----------
74 - nr_periods: Number of enforcement intervals that have elapsed.
75 - nr_throttled: Number of times the group has been throttled/limited.
76 - throttled_time: The total time duration (in nanoseconds) for which entities
79 This interface is read-only.
82 ---------------------------
84 attainable, that is: max(c_i) <= C. However, over-subscription in the
85 aggregate case is explicitly allowed to enable work-conserving semantics
102 ---------------------------
109 The fact that cpu-local slices do not expire results in some interesting corner
114 quota as well as the entirety of each cpu-local slice in each period. As a
118 For highly-threaded, non-cpu bound applications this non-expiration nuance
132 possibility of wastefully expiring quota on cpu-local silos that don't need a
135 The interaction between cpu-bound and non-cpu-bound-interactive applications
137 gave each of these applications half of a cpu-core and they both got scheduled
138 on the same CPU it is theoretically possible that the non-cpu bound application
140 cpu-bound application from fully using its quota by that same amount. In these
141 instances it will be up to the CFS algorithm (see sched-design-CFS.rst) to
142 decide which application is chosen to run, as they will both be runnable and
147 --------
156 2. Limit a group to 2 CPUs worth of runtime on a multi-CPU machine