linux-kernel - Re: [RFC PATCH] sched/deadline: show leftover runtime and abs deadline in /proc/-/sched

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Date:   Tue, 25 Oct 2016 12:10:17 +0200
From:   luca abeni <luca.abeni@...tn.it>
To:     Juri Lelli <juri.lelli@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
        Juri Lelli <juri.lelli@...il.com>,
        linux-kernel@...r.kernel.org,
        Daniel Bistrot de Oliveira <danielbristot@...il.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC PATCH] sched/deadline: show leftover runtime and abs
 deadline in /proc/-/sched

On Tue, 25 Oct 2016 10:33:21 +0100
Juri Lelli <juri.lelli@....com> wrote:

> On 25/10/16 11:25, Peter Zijlstra wrote:
> > On Tue, Oct 25, 2016 at 12:32:53AM +0200, Tommaso Cucinotta wrote:  
> > > Hi all,
> > > 
> > > this is a tiny patch providing readings of the current (leftover)
> > > runtime and absolute deadline in /proc/*/sched. Mostly useful for
> > > debugging, I heard others playing with SCHED_DEADLINE had some
> > > need for similar patches as well.
> > > 
> > > In addition to debugging, reading the leftover runtime is
> > > generally useful for adaptive/incremental RT logics that need to
> > > check whether there's enough runtime left for refining the
> > > computed result, or just use what we've computed so far and block
> > > till the next instance. Also, knowing what the absolute
> > > scheduling deadline is (along with what clock it refers to) might
> > > be useful for synchronization purposes. (albeit, for real
> > > production code, I wouldn't like to parse /proc anyway, rather
> > > I'd prefer to retrieve those params via eg
> > > sched_getscheduler()?)  
> > 
> > So for programmatic use, this interface is not recommended. For
> > debugging this is fine.
> > 
> > Not sure what form the programmatic interface should take, we have
> > precedence in sys_sched_rr_get_interval() for a syscall (we could
> > even abuse this one).
> > 
> > Anybody any ideas?
> >   
> 
> Maybe extend getattr() to return actual runtime params? (instead of
> the static ones, or along to them)

This is similar to what I did in the past: I used (or maybe abused?)
the "flags" argument of getattr() to tell it if I wanted it to return
the current runtime and scheduling deadline, or the maximum runtime and
relative deadline.

I think that both the "/proc based" interface proposed by Tommaso and
the syscall-based one are useful (for different purposes).


				Luca