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Documentation: sched/RT: Update paragraphs about RT bandwidth control

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This has slightly changed with the introduction of fair_server.
Update the most relevant parts.

Link: https://lore.kernel.org/r/Z0c8S8i3qt7SEU14@jlelli-thinkpadt14gen4.remote.csb/
Signed-off-by: Michal Koutný <mkoutny@suse.com>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20241211170052.2449581-1-mkoutny@suse.com
This commit is contained in:
Michal Koutný 2024-12-11 18:00:52 +01:00 committed by Jonathan Corbet
parent 80568f479b
commit bbf5254a5a
2 changed files with 11 additions and 10 deletions
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13
Documentation/scheduler/sched-deadline.rst
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@ -591,12 +591,13 @@ Deadline Task Scheduling
The system wide settings are configured under the /proc virtual file system. The system wide settings are configured under the /proc virtual file system.
For now the -rt knobs are used for -deadline admission control and the For now the -rt knobs are used for -deadline admission control and with
-deadline runtime is accounted against the -rt runtime. We realize that this CONFIG_RT_GROUP_SCHED the -deadline runtime is accounted against the (root)
isn't entirely desirable; however, it is better to have a small interface for -rt runtime. With !CONFIG_RT_GROUP_SCHED the knob only serves for the -dl
now, and be able to change it easily later. The ideal situation (see 5.) is to admission control. We realize that this isn't entirely desirable; however, it
run -rt tasks from a -deadline server; in which case the -rt bandwidth is a is better to have a small interface for now, and be able to change it easily
direct subset of dl_bw. later. The ideal situation (see 5.) is to run -rt tasks from a -deadline
server; in which case the -rt bandwidth is a direct subset of dl_bw.
This means that, for a root_domain comprising M CPUs, -deadline tasks This means that, for a root_domain comprising M CPUs, -deadline tasks
can be created while the sum of their bandwidths stays below: can be created while the sum of their bandwidths stays below:

8
Documentation/scheduler/sched-rt-group.rst
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@ -92,10 +92,10 @@ The system wide settings are configured under the /proc virtual file system:
/proc/sys/kernel/sched_rt_runtime_us: /proc/sys/kernel/sched_rt_runtime_us:
A global limit on how much time real-time scheduling may use. This is always A global limit on how much time real-time scheduling may use. This is always
less or equal to the period_us, as it denotes the time allocated from the less or equal to the period_us, as it denotes the time allocated from the
period_us for the real-time tasks. Even without CONFIG_RT_GROUP_SCHED enabled, period_us for the real-time tasks. Without CONFIG_RT_GROUP_SCHED enabled,
this will limit time reserved to real-time processes. With this only serves for admission control of deadline tasks. With
CONFIG_RT_GROUP_SCHED=y it signifies the total bandwidth available to all CONFIG_RT_GROUP_SCHED=y it also signifies the total bandwidth available to
real-time groups. all real-time groups.
* Time is specified in us because the interface is s32. This gives an * Time is specified in us because the interface is s32. This gives an
operating range from 1us to about 35 minutes. operating range from 1us to about 35 minutes.