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Date: Thu, 23 Aug 2018 15:30:15 +0200
From: luca abeni <luca.abeni@santannapisa.it>
Subject: Re: SCHED_DEADLINE as user
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To: Juri Lelli <juri.lelli@gmail.com>
Cc: Tim Blechmann <tim@klingt.org>, Daniel Bristot de Oliveira <daniel@bristot.me>, linux-rt-users@vger.kernel.org, Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>

On Thu, 23 Aug 2018 15:09:57 +0200
Juri Lelli <juri.lelli@gmail.com> wrote:

> On 23/08/18 15:00, luca abeni wrote:
> > On Thu, 23 Aug 2018 14:37:39 +0200
> > Juri Lelli <juri.lelli@gmail.com> wrote:
> > [...]  
> > > > > Maybe the existing system wide sched_rt_{period,
> > > > > runtime}_us are enough?    
> > > > 
> > > > I do not know... A cgroup-based interface looks more powerful
> > > > (and not so difficult to implement... :), and would allow the
> > > > sysadmin to decide which users can use SCHED_DEADLINE, how much
> > > > SCHED_DEADLINE bandwidth can each user/group use, etc...    
> > > 
> > > How about extending PAM limits instead? It looks like it's what
> > > (e.g.) audio users rely on already [1]. It is maybe possible to
> > > add dlruntime, dlperiod, dldeadline parameters in there?  
> > 
> > Ok, I do not know much about these PAM limits... Where can I find
> > more information?  
> 
> The link I shared already gives some information, man pam_limits and
> limits.conf also.
> 
> > What do we need to implement exactly, to add these dlruntime,
> > dlperiod, dldeadline parameters?  
> 
> Not sure yet "exactly" :-), but I'd say something along these lines
> 
> https://elixir.bootlin.com/linux/latest/source/kernel/sched/core.c#L4198

Ok, thanks; I think I got it: we need to extend the "rlim" array (in
signal_struct) adding fields for "RLIMIT_DLRUNTIME" and friends
(actually, I think a "RLIMIT_UTILIZATION" field is also needed). And
then we need to add checks for these fields in __sched_setscheduler(),
etc...

Maybe I am misunderstanding this stuff, but the cgroup-based approach
looks simpler / more elegant :)



			Thanks,
				Luca