Messages in this thread |  | | Date | Sat, 22 Sep 2001 20:14:50 -0700 | From | george anzinger <> | Subject | Re: [PATCH] Preemption Latency Measurement Tool |
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Robert Love wrote: > > On Sat, 2001-09-22 at 19:40, safemode wrote: > > ok. The preemption patch helps realtime applications in linux be a little > > more close to realtime. I understand that. But your mp3 player shouldn't > > need root permission or renicing or realtime priority flags to play mp3s. > > It doesn't, it needs them to play with a dbench 32 running in the > background. This isn't nessecarily acceptable, either, but it is a > difference. > > Note one thing the preemption patch does is really make `realtime' apps > accel. Without it, regardless of the priority of the application, the > app can be starved due to something in kernel mode. Now it can't, and > since said application is high priority, it will get the CPU when it > wants it. > > This is not to say the preemption patch is no good if you don't run > stuff at realtime -- I don't (who uses nice, anyhow? :>), and I notice > a difference. > > > To > > test how well the latency patches are working you should be running things > > all at the same priority. The main issue people are having with skipping > > mp3s is not in the decoding of the mp3 or in the retrieving of the file, it's > > in the playing in the soundcard. That's being affected by dbench flooding > > the system with irq requests. I'm inclined to believe it's irq requests > > because the _only_ time i have problems with mp3s (and i dont change priority > > levels) is when A. i do a cdparanoia -Z -B "1-" or dbench 32. I bet if > > someone did these tests on scsi hardware with the latency patch, they'd find > > much better results than us users of ide devices. > > The skips are really big to be irq requests, although perhaps you are > right in that the handling of the irq (we disable preemption during > irq_off, of course, but also during bottom half execution) is the > problem. > > However, I am more inclined to believe it is something else. All these > long held locks can indeed be the problem. > > I am on an all UW2 SCSI system, and I have no major blips playing during > a `dbench 16' (never ran 32). However, many other users (Dieter, I > believe) are on a SCSI system too.
Dieter, could you post your .config file? It might have a clue or two.
George
> > > even i dont get any skips when i run the player at nice -n -20. That > > doesn't tell you much about the preemption patch though. And it doesn't tell > > you about performance when you dont give linux the chance to do what it does, > > multitask. That's where the latency patch is directed at improving, i > > think. > > Agreed. > > -- > Robert M. Love > rml at ufl.edu > rml at tech9.net - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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