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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 26 Jan 2009 08:25:45 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jussi Laako <jussi@...arnerd.net>
Cc:	James Courtier-Dutton <James@...erbug.co.uk>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH] Multimedia scheduling class

On Mon, 2009-01-26 at 01:09 +0200, Jussi Laako wrote:
> James Courtier-Dutton wrote:
> >> 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.
> > 
> > There is never a need for media players to use this.
> > Media players have time stamps on the displayed frames.
> > If the timestamp on a frame indicates it has taken too long to decode
> > it, the media player just skips the frame until it reaches frames that
> > have non-expired time stamps. No need for any kernel help here.
> 
> This is completely irrelevant. These media players still play audio and
> sync video to audio. Many of these players are not programmed in a way
> that it would be safe to run these on SCHED_FIFO. Or the environment
> these are running in is not safe enough. But still smooth video and
> audio playback is needed, even in cases when locate database is being
> rebuilt in the background and possibly other CPU and IO intensive tasks
> are running. Any skipped frames make the video playback look jumpy, if
> frames are lost, it should be single frame periodically, not burst of
> frames at once...
> 
> Good everyday normal example is HD video played from Youtube or similar
> site using Flash plugin inside browser. There can be various background
> tasks running at the same time, but the video playback should still be
> smooth. One may want to run thread doing video decoding at significantly
> lower priority than audio decoding thread in order to maintain overall
> system responsiveness in cases of high CPU load from the video decoding
> part. While the audio thread shouldn't starve or miss it's deadline.

Right, and I think the solution to this problem is twofold, 1)
application writers should start writing (soft) realtime applications if
they want (soft) realtime behaviour -- there's just no way around that.

And 2), the kernel can help by providing a deadline based scheduler,
which should make the above easier and less likely to mess up the rest
of the system. ie. a deadline scheduled application will not exceed its
allotted budget, unlike a FIFO scheduled app.



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/