Re: ck vs. cfs : realtime audio performance

[Lenar Lõhmus <lenar@city.ee>]

Cc'd to LKML & Ingo.

L.

Klaus Schulz wrote:
> Hi there.
>
>
>
>
> Am Dienstag, den 31.07.2007, 10:26 +0200 schrieb Klaus Schulz:
>   
> > Hi folks.
> >
> > I am currently testing the 2.6.22.1 cfs-rt9 vs. ck1 on my rather pure
> > realtime high-end-audio setup. (NO X, just a terminal, streaming .wav. 
> > I am using my own written player and brutefir as the audio engine.)
> > Comment: This is not a standard (amarok or xmms setup), all buffers in
> > the chain are very small. Any problem will immidetialy end up in xruns.
> > The sounddriver, HW (pci-bus etc.) are tweaked accordingly 
> >
> > Until now ck1 on 2.6.22 is giving me better results (less audible
> > distortions) and runs extremely stable compared to cfs. 
> > Under ck I ran my player with schedtool -R -p 98, which was better than
> > running it e.g. with nice -20 
> > Both setups under cfs were giving me worse results than ck.
> > With CFS I also experienced XRUNS from time to time, what never happened
> > with ck.
> >
> > However:
> >
> > When looking at the latest performance statistics cfs vs. ck which are
> > spread around here, I am wondering, what might cause the differences.
> >
> > With ck I tweaked the rr_interval to 6 and was running at 10000Hz,
> > which caused obvious improvements.
> >
> > These options I do not have with CFS.
> >
> > I am wondering if sched_granularity_ns should be touched when using cfs.
> > I googled somewhere that bringing it down to e.g. 250000 instead of
> > 4000000 would smoothen the audio playback. I havn't tried it yet. I am
> > wondering if this tweak is still applicable.
> >     
>
>
>
> I did test now decreasing the sched_granularity_ns to 250000.
> There is still a clearly audible difference comparing ck and cfs. 
> ck Ídelivers cristal clear sound. With cfs I still get quite some
> distortions. 
>
> Any hints how to improve the situtation are welcome. 
>
>
>
>   
> > I'd be happy to get a hint on how to tweak the system parameters best to
> > give cfs a fair chance. I am also wondering how the timer freqency could
> > by increased under a cfs-patched kernel.
> >
> > Info: dynamic ticks and IRQ balancing are off for the time being.
> >      /proc/sys/dev/rtc is set to 4096 (gave me best results)
> >      ( I don't have a clue how all the (rtc)-timers in the OS interact,
> >        To me it is just a trial and error exercise to figure out which
> >        setup sounds best)
> >
> > THX for your advise. 
> >
> > Cheers
> > \Klaus
> >     
>
>
> Cheers
> \Klaus
>
>
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>   

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