diff options
Diffstat (limited to 'Documentation/scheduler')
| -rw-r--r-- | Documentation/scheduler/00-INDEX | 2 | ||||
| -rw-r--r-- | Documentation/scheduler/sched-rt-group.txt | 59 |
2 files changed, 61 insertions, 0 deletions
diff --git a/Documentation/scheduler/00-INDEX b/Documentation/scheduler/00-INDEX index b5f5ca069b2d..fc234d093fbf 100644 --- a/Documentation/scheduler/00-INDEX +++ b/Documentation/scheduler/00-INDEX @@ -12,5 +12,7 @@ sched-domains.txt - information on scheduling domains. sched-nice-design.txt - How and why the scheduler's nice levels are implemented. +sched-rt-group.txt + - real-time group scheduling. sched-stats.txt - information on schedstats (Linux Scheduler Statistics). diff --git a/Documentation/scheduler/sched-rt-group.txt b/Documentation/scheduler/sched-rt-group.txt new file mode 100644 index 000000000000..1c6332f4543c --- /dev/null +++ b/Documentation/scheduler/sched-rt-group.txt @@ -0,0 +1,59 @@ + + +Real-Time group scheduling. + +The problem space: + +In order to schedule multiple groups of realtime tasks each group must +be assigned a fixed portion of the CPU time available. Without a minimum +guarantee a realtime group can obviously fall short. A fuzzy upper limit +is of no use since it cannot be relied upon. Which leaves us with just +the single fixed portion. + +CPU time is divided by means of specifying how much time can be spent +running in a given period. Say a frame fixed realtime renderer must +deliver 25 frames a second, which yields a period of 0.04s. Now say +it will also have to play some music and respond to input, leaving it +with around 80% for the graphics. We can then give this group a runtime +of 0.8 * 0.04s = 0.032s. + +This way the graphics group will have a 0.04s period with a 0.032s runtime +limit. + +Now if the audio thread needs to refill the DMA buffer every 0.005s, but +needs only about 3% CPU time to do so, it can do with a 0.03 * 0.005s += 0.00015s. + + +The Interface: + +system wide: + +/proc/sys/kernel/sched_rt_period_ms +/proc/sys/kernel/sched_rt_runtime_us + +CONFIG_FAIR_USER_SCHED + +/sys/kernel/uids/<uid>/cpu_rt_runtime_us + +or + +CONFIG_FAIR_CGROUP_SCHED + +/cgroup/<cgroup>/cpu.rt_runtime_us + +[ time is specified in us because the interface is s32; this gives an + operating range of ~35m to 1us ] + +The period takes values in [ 1, INT_MAX ], runtime in [ -1, INT_MAX - 1 ]. + +A runtime of -1 specifies runtime == period, ie. no limit. + +New groups get the period from /proc/sys/kernel/sched_rt_period_us and +a runtime of 0. + +Settings are constrained to: + + \Sum_{i} runtime_{i} / global_period <= global_runtime / global_period + +in order to keep the configuration schedulable. |