linux-kernel - Re: [RFC PATCH 0/3] CFS idle injection

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Message-ID: <20151110105634.GA8516@e106622-lin>
Date:	Tue, 10 Nov 2015 10:56:34 +0000
From:	Juri Lelli <juri.lelli@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Juri Lelli <juri.lelli@...il.com>,
	Punit Agrawal <punit.agrawal@....com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Paul Turner <pjt@...gle.com>, Len Brown <len.brown@...el.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andi Kleen <andi.kleen@...el.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH 0/3] CFS idle injection

On 11/10/15, Peter Zijlstra wrote:
> On Tue, Nov 10, 2015 at 10:07:35AM +0000, Juri Lelli wrote:
> > Do you think that using SCHED_DEADLINE here would be completely
> > foolish? I mean, we would have the duty_cycle/period thing for free, it
> > would be know to the scheduler (as to maybe address Thomas' concerns)
> > and we could think to make idle injection part of system analysis (for
> > the soft-RT use cases).
> 
> DEADLINE would be awesome, but I think we need work on two fronts before
> we can really sell it as the awesome that it is ;-)
> 
>  - greedy and or statistical bounds
>  - !priv
> 
> The first is such that we can better deal with the erratic nature of
> media decode without going full worst case on it, and the second just
> makes it so much more accessible.
> 

Right. For the first point I think we just need to make our off-line
calculation right, not that we need to modify implementation. On the
second point we need more work yes. Also, another thing that is missing
is frequency (uarch) scaling for reservations parameters, something alike
what we are doing for CFS; this last point might be solved sooner :-).

Thanks,

- Juri

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