Date: Tue, 25 Oct 2016 11:25:19 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Tommaso Cucinotta <tommaso.cucinotta@sssup.it>
Cc: Luca Abeni <luca.abeni@unitn.it>, Juri Lelli <juri.lelli@gmail.com>,
        linux-kernel@vger.kernel.org, linux-dl@retis.sssup.it,
        Daniel Bistrot de Oliveira <danielbristot@gmail.com>,
        Ingo Molnar <mingo@kernel.org>
Subject: Re: [RFC PATCH] sched/deadline: show leftover runtime and abs
 deadline in /proc/-/sched
Message-ID: <20161025092519.GV3102@twins.programming.kicks-ass.net>
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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?