Are there some methods that could limit how much CPU resources could be a single Xenomai process or thread?

Lange Norbert norbert.lange at andritz.com
Mon Jul 20 10:31:23 CEST 2020


Hello,

I am reconnecting the ML.


I am not aware of any good documentation for SCHED_TP,
but there is an example in smokey/sched-tp which Id use as starting point.

I don’t think SCHED_TP will measurable affect latency, outside of course in
the case where its “by design” (process needs to wait for its timeslice).

Norbert

From: 孙世龙 sunshilong <sunshilong369 at gmail.com>
Sent: Samstag, 18. Juli 2020 07:51
To: Lange Norbert <norbert.lange at andritz.com>
Cc: Meng, Fino <fino.meng at intel.com>
Subject: Re: Are there some methods that could limit how much CPU resources could be a single Xenomai process or thread?

Hi, Norbert

Thank you for the clarification.

>You can do something similar with the  temporal partitioning scheduler (SCHED_TP),
>cgroups uses a similar concept of "time-slices", but is less strict AFAIU
Does SCHED_TP enlarge the latency(compared to SCHED_FIFO)?

Do you have more information about SCHED_TP?  If the answer is yes,
could you please suggest some documents for me to go through?

I searched all the source code of the Xenomai project and checked
the help information from the Kconfig, but no useful information about
SCHED_TP was found.
I googled it, only found this:
The SCHED_TP policy divides the scheduling time into a recurring
global frame, which is itself divided into an arbitrary number of time
partitions. Only threads assigned to the current partition are deemed
runnable, and scheduled according to a FIFO-based rule within this
partition. When completed, the current partition is advanced
automatically to the next one by the scheduler, and the global time
frame recurs from the first partition defined, when the last partition
has ended.

Thank you for your attention to this matter.
Best Regards.
Sunshilong(孙世龙)
On Fri, Jul 17, 2020 at 6:44 PM Lange Norbert <norbert.lange at andritz.com<mailto:norbert.lange at andritz.com>> wrote:


> -----Original Message-----
> From: Xenomai <xenomai-bounces at xenomai.org<mailto:xenomai-bounces at xenomai.org>> On Behalf Of ???
> sunshilong via Xenomai
> Sent: Freitag, 17. Juli 2020 12:18
> To: Meng, Fino <fino.meng at intel.com<mailto:fino.meng at intel.com>>
> Cc: Xenomai (xenomai at xenomai.org<mailto:xenomai at xenomai.org>) <xenomai at xenomai.org<mailto:xenomai at xenomai.org>>
> Subject: Re: Are there some methods that could limit how much CPU
> resources could be a single Xenomai process or thread?
>
> NON-ANDRITZ SOURCE: BE CAUTIOUS WITH CONTENT, LINKS OR
> ATTACHMENTS.
>
>
> Hi, 孟祥夫
> Thank you for taking the time to respond to my question.
>
> >In my understanding cgroup's design is exclusionary with real-
> time/deterministic/time coordinate design.
> >The latency/jitter is already down to 20us level,  how it can endure cgroup's
> volatility.
> I don't hold much hope, either. But I am not sure whether it's impossible to
> achieve this goal or not.

You can do something similar with the  temporal partitioning scheduler (SCHED_TP),
cgroups uses a similar concept of "time-slices", but is less strict AFAIU

Norbert

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