linux-kernel - Re: [RFC][PATCH] Multimedia scheduling class

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Date:	Tue, 13 Jan 2009 11:44:52 +0200
From:	Jussi Laako <jussi@...arnerd.net>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH] Multimedia scheduling class

Peter Zijlstra wrote:
> 
> Well, that's not my problem is it ;-), just batter them with a
> clue-stick, no need to fudge the kernel for that.

Sure, been doing that already... :)
There's just sort of a huge gap between rt-schedulers and the normal
scheduler.

> Right, which is where deadline scheduling would be nice. Once you start
> running into the budget throttle you know you've got to start dropping
> frames in order to keep up.
> 
> The proposal is for it to start sending SIGXCPU once it starts
> throttling tasks in order to notify them of missed deadlines etc.

For sure this is nice for certain tasks. I'm not entirely convinced if
the average media player or Flash-plugin would or should start using these.

I believe both approaches could co-exist to address different needs.
SCHED_MM is for the average software and is in a sense similar to
SCHED_BATCH and SCHED_IDLE, just targeting different use cases.
Modification is reasonably small and shouldn't have any impact when not
used. Deadline scheduler would probably belong to the
SCHED_RR/SCHED_FIFO family?

> Like said, deadline schedulers can help here. You can even dynamically
> adjust the parameters -- eg. fall back to half frame rate but double
> budget or something.

Managing the budget in an average system will be painful. In a
completely embedded environment this is of course rather straightforward.
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