Commit bbf5254a authored by Michal Koutný's avatar Michal Koutný Committed by Jonathan Corbet
Browse files

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

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: default avatarMichal Koutný <mkoutny@suse.com>
Reviewed-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Acked-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20241211170052.2449581-1-mkoutny@suse.com
parent 80568f47

Documentation/scheduler/sched-deadline.rst

+7 −6
Original line number Diff line number Diff line
@@ -591,12 +591,13 @@ Deadline Task Scheduling 


 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

 -deadline runtime is accounted against the -rt runtime. We realize that this

 isn't entirely desirable; however, it is better to have a small interface for

 now, and be able to change it easily 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.

 For now the -rt knobs are used for -deadline admission control and with

 CONFIG_RT_GROUP_SCHED the -deadline runtime is accounted against the (root)

 -rt runtime. With !CONFIG_RT_GROUP_SCHED the knob only serves for the -dl

 admission control. We realize that this isn't entirely desirable; however, it

 is better to have a small interface for now, and be able to change it easily

 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

 can be created while the sum of their bandwidths stays below:

Documentation/scheduler/sched-rt-group.rst

+4 −4
Original line number Diff line number Diff line
@@ -92,10 +92,10 @@ The system wide settings are configured under the /proc virtual file system: 
/proc/sys/kernel/sched_rt_runtime_us:

  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

  period_us for the real-time tasks. Even without CONFIG_RT_GROUP_SCHED enabled,

  this will limit time reserved to real-time processes. With

  CONFIG_RT_GROUP_SCHED=y it signifies the total bandwidth available to all

  real-time groups.

  period_us for the real-time tasks. Without CONFIG_RT_GROUP_SCHED enabled,

  this only serves for admission control of deadline tasks. With

  CONFIG_RT_GROUP_SCHED=y it also signifies the total bandwidth available to

  all real-time groups.



  * Time is specified in us because the interface is s32. This gives an

    operating range from 1us to about 35 minutes.