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 10:33:21 +0100
From:   Juri Lelli <juri.lelli@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
        Luca Abeni <luca.abeni@...tn.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 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)