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sched/rt/docs: Clarify & fix sched_rt_* sysctl docs 

- Describe explicitly that sched_rt_runtime_us is allocated from
  sched_rt_period_us and hence always less or equal to that value.

- The limit for sched_rt_runtime_us is not INT_MAX-1, but rather it's
  limited by the value of sched_rt_period_us. If sched_rt_period_us is
  INT_MAX then sched_rt_runtime_us can be set to INT_MAX as well.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231002115553.3007-3-chrubis@suse.cz
This commit is contained in:
Cyril Hrubis 2023-10-02 13:55:52 +02:00 committed by Ingo Molnar
parent 079be8fc63
commit e6dbdd8fb7
1 changed files with 8 additions and 6 deletions
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14
Documentation/scheduler/sched-rt-group.rst
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@ -87,18 +87,20 @@ lack an EDF scheduler to make non-uniform periods usable.
The system wide settings are configured under the /proc virtual file system:
/proc/sys/kernel/sched_rt_period_us:
The scheduling period that is equivalent to 100% CPU bandwidth
The scheduling period that is equivalent to 100% CPU bandwidth.
/proc/sys/kernel/sched_rt_runtime_us:
A global limit on how much time realtime scheduling may use. Even without
CONFIG_RT_GROUP_SCHED enabled, this will limit time reserved to realtime
processes. With CONFIG_RT_GROUP_SCHED it signifies the total bandwidth
available to all realtime groups.
A global limit on how much time realtime scheduling may use. This is always
less or equal to the period_us, as it denotes the time allocated from the
period_us for the realtime tasks. Even without CONFIG_RT_GROUP_SCHED enabled,
this will limit time reserved to realtime processes. With
CONFIG_RT_GROUP_SCHED=y it signifies the total bandwidth available to all
realtime groups.
* Time is specified in us because the interface is s32. This gives an
operating range from 1us to about 35 minutes.
* sched_rt_period_us takes values from 1 to INT_MAX.
* sched_rt_runtime_us takes values from -1 to (INT_MAX - 1).
* sched_rt_runtime_us takes values from -1 to sched_rt_period_us.
* A run time of -1 specifies runtime == period, ie. no limit.