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

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Message-ID: <20150131095659.GD32343@twins.programming.kicks-ass.net>
Date:	Sat, 31 Jan 2015 10:56:59 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Juri Lelli <juri.lelli@....com>
Cc:	Luca Abeni <luca.abeni@...tn.it>, Kirill Tkhai <tkhai@...dex.ru>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Another SCHED_DEADLINE bug (with bisection and possible fix)

On Fri, Jan 30, 2015 at 10:35:02AM +0000, Juri Lelli wrote:
> So, we do the safe thing only in case of throttling.

No, even for the !throttle aka running tasks. We only use
dl_{runtime,deadline,period} for replenishment, until that time we
observe the old runtime/deadline set by the previous replenishment.

> I guess is more than
> ok for now, while we hopefully find some spare cycle to implement a
> complete solution :/.

Yeah, I bet the fun part is computing the 0-lag across the entire root
domain, per-cpu 0-lag isn't correct afaict.
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