linux-kernel - Re: [RFC][PATCH] sched: Kick bandwidth timer immediately on start up

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Message-ID: <20160218091528.6c05c181@gandalf.local.home>
Date:	Thu, 18 Feb 2016 09:15:28 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Clark Williams <williams@...hat.com>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	John Kacur <jkacur@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH] sched: Kick bandwidth timer immediately on start
 up

On Tue, 16 Feb 2016 18:37:46 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> A better solution may be to subtract the bandwidth that the deadline
> task uses from the rt_runtime, and add it back when its finished. Then
> there wont be a need for runtime tracking of the time used by deadline
> tasks.
> 
> I may play with that solution tomorrow.
> 

OK, so I played with this solution. It's much more complex than I was
hoping it to be. The main issue is there's no one to one relationship
with the deadline bandwidth and the rt bandwidth. Each runqueue has its
own rt ratio, but each root domain that has its own deadline ratio.
Thus, when you add to the dl ratio, it makes adding that to the rt
bandwidths that more complex. It's doable, but it will make getting the
dl_bw right with new root domains harder than it already is, and that
is currently not working.

My recommendation is to hold off on a better solution till we can find a
way to merge rt bandwidth with the Constant Bandwidth Server (CBS).

Thus, please accept this current patch as it appears to fix the problem
without any other side effects that I can find.

-- Steve