linux-kernel - Re: [RFC 4/8] Improve the tracking of active utilisation

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Message-ID: <20160115102740.00068482@luca-1225C>
Date:	Fri, 15 Jan 2016 10:27:40 +0100
From:	Luca Abeni <luca.abeni@...tn.it>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@....com>
Subject: Re: [RFC 4/8] Improve the tracking of active utilisation

On Thu, 14 Jan 2016 20:43:23 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, Jan 14, 2016 at 04:24:49PM +0100, Luca Abeni wrote:
> > This patch implements a more theoretically sound algorithm for
> > thracking the active utilisation: instead of decreasing it when a
> > task blocks, use a timer (the "inactive timer", named after the
> > "Inactive" task state of the GRUB algorithm) to decrease the
> > active utilisaation at the so called "0-lag time".
> 
> See also the large-ish comment in __setparam_dl().
> 
> If we go do proper 0-lag, as GRUB requires, then we might as well use
> it for that.
Yes, I initially tried to do this, but I found some issues (I do not
remember, but I think they were related to tasks moving from
SCHED_DEADLINE to SCHED_OTHER, and then migrating to some other
runqueue while SCHED_OTHER but before the 0-lag time)

I'll search my notes for this issue in the next days and check
again (maybe when I wrote this code I was just misunderstanding
something)


			Luca

> 
> But we need to sort the issue of the task exiting with an armed timer.
> The solution suggested there is keeping a task reference with the
> timer.