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

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Date:	Tue, 19 Jan 2016 13:20:13 +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

Hi Peter,

On 01/14/2016 08:43 PM, Peter Zijlstra 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.
Just to check if I understand correctly:
I would need to remove "dl_b->total_bw -= p->dl.dl_bw;" from task_dead_dl(),
and __dl_clear() from "else if (!dl_policy(policy) && task_has_dl_policy(p))"
in dl_overflow(). Then, arm the inactive_timer in these cases, and add the
__dl_clear() in the "if (!dl_task(p))" in inactive_task_timer()... Right?

If this understanding is correct (modulo some details that I'll figure out
during testing), I'll try this.

In theory, the inactive_timer would be the right place to also decrease
the active utilisation when a task switches from SCHED_DEADLINE to something
else... But this is problematic if the task migrates after switching from
SCHED_DEADLINE and before the timer fires.



			Thanks,
				Luca