RE: cgroups CPU time management + PREEMPT_RT

RE: cgroups CPU time management + PREEMPT_RT

[Elana Copperman]

Hi,
We are new to the mailing list, and new to PREEMPT_RT.
We are working on a project with a safety requirement to configure cgroups for resource management, as well as functional requirement for deployment of PREEMPT_RT patch.
cgroups in general can be used in this context, in particular for managing resources such as memory; and even for managing CPU time for non-RT tasks.  
However, we do see a potential problem with RT tasks, and how the CPU controller would work with the RT scheduling.
There is some obvious concern here, and this seems to be backed by what I find online regarding this question.

Can you help us to clarify what is the current state of implementation, and if there is any support for cgroup CPU controller configuration to work effectively with PREEMPT_RT for RT tasks?  
Thanks 
Elana

Re: cgroups CPU time management + PREEMPT_RT

[Elana Copperman]

Hi, can you help to clarify if there is any implementation support or evidence on configuring cgroups CPU time allocations for RT tasks in conjunction with the PREEMPT_RT patch?

Or are the two requirements contradictory in essence and not jointly feasible?

Thanks

Elana and Vladimir




From: Elana Copperman

Sent: Thursday, May 7, 2020 10:08 PM

To: linux-rt-users <linux-rt-users@vger.kernel.org>; Vladimir Kondratiev (Mobileye) <63dc4b5d-c467-4bfb-bce5-74485907c850@intel.mail.onmicrosoft.com>

Subject: RE: cgroups CPU time management + PREEMPT_RT

 


Hi,

We are new to the mailing list, and new to PREEMPT_RT.

We are working on a project with a safety requirement to configure cgroups for resource management, as well as functional requirement for deployment of PREEMPT_RT patch.

cgroups in general can be used in this context, in particular for managing resources such as memory; and even for managing CPU time for non-RT tasks. 


However, we do see a potential problem with RT tasks, and how the CPU controller would work with the RT scheduling.

There is some obvious concern here, and this seems to be backed by what I find online regarding this question.



Can you help us to clarify what is the current state of implementation, and if there is any support for cgroup CPU controller configuration to work effectively with PREEMPT_RT for RT tasks? 


Thanks 

Elana

Re: cgroups CPU time management + PREEMPT_RT

[Steven Rostedt]

On Tue, 12 May 2020 13:30:27 +0000
Elana Copperman <Elana.Copperman@mobileye.com> wrote:

> Hi, can you help to clarify if there is any implementation support or
> evidence on configuring cgroups CPU time allocations for RT tasks in
> conjunction with the PREEMPT_RT patch?

What exactly are you trying to do with cgroups CPU time allocations, and
what is the problem you are seeing with the PREEMPT_RT patch with them?

I'm assuming you are using the 5.6-rt kernel.

-- Steve


> 
> Or are the two requirements contradictory in essence and not jointly
> feasible?
> 
> Thanks
> 
> Elana and Vladimir
> 
> 
> 
> 
> From: Elana Copperman
> 
> Sent: Thursday, May 7, 2020 10:08 PM
> 
> To: linux-rt-users <linux-rt-users@vger.kernel.org>; Vladimir Kondratiev
> (Mobileye)
> <63dc4b5d-c467-4bfb-bce5-74485907c850@intel.mail.onmicrosoft.com>
> 
> Subject: RE: cgroups CPU time management + PREEMPT_RT
> 
>  
> 
> 
> Hi,
> 
> We are new to the mailing list, and new to PREEMPT_RT.
> 
> We are working on a project with a safety requirement to configure
> cgroups for resource management, as well as functional requirement for
> deployment of PREEMPT_RT patch.
> 
> cgroups in general can be used in this context, in particular for
> managing resources such as memory; and even for managing CPU time for
> non-RT tasks. 
> 
> 
> However, we do see a potential problem with RT tasks, and how the CPU
> controller would work with the RT scheduling.
> 
> There is some obvious concern here, and this seems to be backed by what I
> find online regarding this question.
> 
> 
> 
> Can you help us to clarify what is the current state of implementation,
> and if there is any support for cgroup CPU controller configuration to
> work effectively with PREEMPT_RT for RT tasks? 
> 
> 
> Thanks 
> 
> Elana
> 
> 
> 
> 
> 

RE: cgroups CPU time management + PREEMPT_RT

[Elana Copperman]

-----Original Message-----
From: Steven Rostedt <rostedt@goodmis.org> 
Sent: Tuesday, May 12, 2020 4:36 PM
To: Elana Copperman <Elana.Copperman@mobileye.com>
Cc: linux-rt-users <linux-rt-users@vger.kernel.org>; Thomas Gleixner <tglx@linutronix.de>; Vladimir Kondratiev (Mobileye) <63dc4b5d-c467-4bfb-bce5-74485907c850@intel.mail.onmicrosoft.com>
Subject: Re: cgroups CPU time management + PREEMPT_RT

On Tue, 12 May 2020 13:30:27 +0000
Elana Copperman <Elana.Copperman@mobileye.com> wrote:

> Hi, can you help to clarify if there is any implementation support or 
> evidence on configuring cgroups CPU time allocations for RT tasks in 
> conjunction with the PREEMPT_RT patch?

What exactly are you trying to do with cgroups CPU time allocations, and what is the problem you are seeing with the PREEMPT_RT patch with them?

I'm assuming you are using the 5.6-rt kernel.

>> No, we are using version 4.19.72 + PREEMPT_RT patch
>> We are still in design stage.  Just trying to understand how to reconcile the requirements.
>> Currently we actually see no justification for using cgroups CPU time allocations for RT tasks, unless you have some specific support in more recent versions of the patch or kernel


-- Steve


> 
> Or are the two requirements contradictory in essence and not jointly 
> feasible?
> 
> Thanks
> 
> Elana and Vladimir
> 
> 
> 
> 
> From: Elana Copperman
> 
> Sent: Thursday, May 7, 2020 10:08 PM
> 
> To: linux-rt-users <linux-rt-users@vger.kernel.org>; Vladimir 
> Kondratiev
> (Mobileye)
> <63dc4b5d-c467-4bfb-bce5-74485907c850@intel.mail.onmicrosoft.com>
> 
> Subject: RE: cgroups CPU time management + PREEMPT_RT
> 
>  
> 
> 
> Hi,
> 
> We are new to the mailing list, and new to PREEMPT_RT.
> 
> We are working on a project with a safety requirement to configure 
> cgroups for resource management, as well as functional requirement for 
> deployment of PREEMPT_RT patch.
> 
> cgroups in general can be used in this context, in particular for 
> managing resources such as memory; and even for managing CPU time for 
> non-RT tasks.
> 
> 
> However, we do see a potential problem with RT tasks, and how the CPU 
> controller would work with the RT scheduling.
> 
> There is some obvious concern here, and this seems to be backed by 
> what I find online regarding this question.
> 
> 
> 
> Can you help us to clarify what is the current state of 
> implementation, and if there is any support for cgroup CPU controller 
> configuration to work effectively with PREEMPT_RT for RT tasks?
> 
> 
> Thanks
> 
> Elana
> 
> 
> 
> 
> 

Re: cgroups CPU time management + PREEMPT_RT

[Sebastian Andrzej Siewior]

On 2020-05-12 13:41:03 [+0000], Elana Copperman wrote:
> 
> 

I think you missed to write a reply or I didn't find it.
So if this is about RT_GROUP_SCHED then it is disabled in RT because it
was once broken. Since then people asked about it and I told them to
please test it and report back what the results are but I never got a
reply back.

Sebastian

Re: cgroups CPU time management + PREEMPT_RT

[Elana Copperman]

Thanks, Sebastian, for your reply.
Yes, it is about RT_GROUP_SCHED (and related parameters such as cpu.rt_runtime_us and cpu.rt_period_us).  The documentation  (such as   https://www.kernel.org/doc/Documentation/scheduler/sched-rt-group.txt ) is fuzzy on details and is not dated, so it was not clear if we were missing anything.

Anyhow, thanks for the confirmation.  I think we will go back to the original plan and avoid using cgroups for managing CPU time for RT tasks.   Perhaps with time and experience on the implementation, we may have a better view on how to properly enable this.
Regards
Elana


From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Sent: Tuesday, May 26, 2020 5:33 PM
To: Elana Copperman <Elana.Copperman@mobileye.com>
Cc: Steven Rostedt <rostedt@goodmis.org>; linux-rt-users <linux-rt-users@vger.kernel.org>; Thomas Gleixner <tglx@linutronix.de>; Vladimir Kondratiev (Mobileye) <63dc4b5d-c467-4bfb-bce5-74485907c850@intel.mail.onmicrosoft.com>
Subject: Re: cgroups CPU time management + PREEMPT_RT 
 
On 2020-05-12 13:41:03 [+0000], Elana Copperman wrote:
> 
> 

I think you missed to write a reply or I didn't find it.
So if this is about RT_GROUP_SCHED then it is disabled in RT because it
was once broken. Since then people asked about it and I told them to
please test it and report back what the results are but I never got a
reply back.

Sebastian