Messages in this thread | | | Subject | Re: [RFC][PATCH] Multimedia scheduling class | From | Peter Zijlstra <> | Date | Mon, 26 Jan 2009 08:25:45 +0100 |
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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.
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