[PATCH] Documentation: sched/RT: Update paragraphs about RT bandwidth control

[PATCH] Documentation: sched/RT: Update paragraphs about RT bandwidth control

[Michal Koutný]

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>
---
 Documentation/scheduler/sched-deadline.rst | 13 +++++++------
 Documentation/scheduler/sched-rt-group.rst |  8 ++++----
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/Documentation/scheduler/sched-deadline.rst b/Documentation/scheduler/sched-deadline.rst
index 22838ed8e13aa..a727827b8dd52 100644
--- a/Documentation/scheduler/sched-deadline.rst
+++ b/Documentation/scheduler/sched-deadline.rst
@@ -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:
diff --git a/Documentation/scheduler/sched-rt-group.rst b/Documentation/scheduler/sched-rt-group.rst
index d685609ed3d7a..80b05a3009ea2 100644
--- a/Documentation/scheduler/sched-rt-group.rst
+++ b/Documentation/scheduler/sched-rt-group.rst
@@ -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.
-- 
2.47.0

Re: [PATCH] Documentation: sched/RT: Update paragraphs about RT bandwidth control

[Juri Lelli]

Hi,

On 11/12/24 18:00, Michal Koutný wrote:
> 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>

Looks good to me.

Reviewed-by: Juri Lelli <juri.lelli@redhat.com>

Best,
Juri

Re: [PATCH] Documentation: sched/RT: Update paragraphs about RT bandwidth control

[Jonathan Corbet]

Michal Koutný <mkoutny@suse.com> writes:

> 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>
> ---
>  Documentation/scheduler/sched-deadline.rst | 13 +++++++------
>  Documentation/scheduler/sched-rt-group.rst |  8 ++++----
>  2 files changed, 11 insertions(+), 10 deletions(-)

Applied, thanks.

jon