linux-kernel - Re: periods and deadlines in SCHED

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Date:	Sun, 11 Jul 2010 08:15:23 +0200
From:	Bjoern Brandenburg <bbb@...il.unc.edu>
To:	Raistlin <raistlin@...ux.it>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Song Yuan <song.yuan@...csson.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nicola Manica <nicola.manica@...i.unitn.it>,
	Luca Abeni <lucabe72@...il.it>,
	Claudio Scordino <claudio@...dence.eu.com>,
	Harald Gustafsson <harald.gustafsson@...csson.com>,
	bastoni@...unc.edu, Giuseppe Lipari <lipari@...is.sssup.it>
Subject: Re: periods and deadlines in SCHED_DEADLINE


On Jul 10, 2010, at 9:50 AM, Raistlin wrote:

>> 
>> What are the exact semantics of this extra proposed syscall?
>> 
> Right now, it is:
> task_wait_interval(t) --> "wake me up at the first instant after t when 
> 			   you can give me my full runtime"
> 
>> What exactly are the benefits over not having it, and simply rely on the
>> task to not wake up more often, but if it does have it run into the lack
>> of budget and sort it that way?
>> 
> What you're saying obviously will always work, and it is actually a
> quite common usage pattern (we use it like that a lot! :-)).
> 
> The new syscall might help when it is important for a task to
> synchronize with the budget provisioning mechanism. It might be
> uncommon, but there could be situations --more in hard than in soft
> scenarios-- where you want to be sure that you're next job (and all the
> subsequent ones, if you behave well) will get its full runtime, even if
> this means waiting a little bit.

Isn't this basically sched_yield? Don't run me now, give lower-priority work a chance to complete, let me run again when my budget is replenished.

Otherwise, what are the semantics of sched_yield under EDF? Cycle through equal-deadline jobs? Given sporadic task activations, this is probably not very useful.

- Björn

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