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28    resolution, or the time it takes to handle the budget refresh itself.
42 Realtime scheduling is all about determinism, a group has to be able to rely on
43 the amount of bandwidth (eg. CPU time) being constant. In order to schedule
54 the other realtime groups will not be permitted to use.
56 Any time not allocated to a realtime group will be used to run normal priority
62 have to play some music and respond to input, leaving it with around 80% CPU
67 limit. Now if the audio thread needs to refill the DMA buffer every 0.005s, but
68 needs only about 3% CPU time to do so, it can do with a 0.03 * 0.005s =
73 realtime tasks have explicitly allocated the CPU time they need to perform
77 lack an EDF scheduler to make non-uniform periods usable.
90   The scheduling period that is equivalent to 100% CPU bandwidth
94   CONFIG_RT_GROUP_SCHED enabled, this will limit time reserved to realtime
96   available to all realtime groups.
99     operating range from 1us to about 35 minutes.
100   * sched_rt_period_us takes values from 1 to INT_MAX.
101   * sched_rt_runtime_us takes values from -1 to (INT_MAX - 1).
109 sched_rt_runtime_us (950000 or 0.95s).  This gives 0.05s to be used by
111 realtime tasks will not lock up the machine but leave a little time to recover
112 it.  By setting runtime to -1 you'd get the old behaviour back.
114 By default all bandwidth is assigned to the root group and new groups get the
116 want to assign bandwidth to another group, reduce the root group's bandwidth
117 and assign some or all of the difference to another group.
119 Realtime group scheduling means you have to assign a portion of total CPU
120 bandwidth to the group before it will accept realtime tasks. Therefore you will
121 not be able to run realtime tasks as any user other than root until you have
122 done that, even if the user has the rights to run processes with realtime
130 CPU bandwidth to task groups.
133 to control the CPU time reserved for each control group.
138 Group settings are checked against the following limits in order to keep the
143 For now, this can be simplified to just the following (but see Future plans):
151 There is work in progress to make the scheduling period for each group
155 equal period to its parent. But realistically its not very useful _yet_
156 as its prone to starvation without deadline scheduling.
171 The next project will be SCHED_EDF (Earliest Deadline First scheduling) to bring
172 full deadline scheduling to the linux kernel. Deadline scheduling the above
176 Implementing SCHED_EDF might take a while to complete. Priority Inheritance is
178 the limited static priority levels 0-99. With deadline scheduling you need to
179 do deadline inheritance (since priority is inversely proportional to the
182 This means the whole PI machinery will have to be reworked - and that is one of