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 11:25:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tommaso Cucinotta <tommaso.cucinotta@...up.it>
Cc:     Luca Abeni <luca.abeni@...tn.it>,
        Juri Lelli <juri.lelli@...il.com>,
        linux-kernel@...r.kernel.org, linux-dl@...is.sssup.it,
        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, 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?