linux-kernel - Re: Another SCHED_DEADLINE bug (with bisection and possible fix)

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Message-ID: <20150115122323.GU23965@worktop.programming.kicks-ass.net>
Date:	Thu, 15 Jan 2015 13:23:23 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Luca Abeni <luca.abeni@...tn.it>
Cc:	Kirill Tkhai <tkhai@...dex.ru>, Juri Lelli <juri.lelli@....com>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"juri.lelli@...il.com" <juri.lelli@...il.com>
Subject: Re: Another SCHED_DEADLINE bug (with bisection and possible fix)

On Thu, Jan 15, 2015 at 12:23:43PM +0100, Luca Abeni wrote:
> There are some parts of the patch that I do not understand (for example:
> if I understand well, if the task is not throttled you set dl_new to 1...
> And if it is throttled you change its current runtime and scheduling deadline...
> Why?)
> Anyway, I tested the patch and I confirm that it fixes the hang I originally
> reported.

I'll go look at the patch in a wee bit. But Juri, Luca, could you
describe the correct behaviour?

>From what I understand we should either modify the tasks run/sleep stats
when we change its parameters or we should schedule a delayed release of
the bandwidth delta (when it reaches its 0-lag point, if thats in the
future).

Doing neither will allow one to game the reservation system afaict.
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