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List:       fedora-devel-list
Subject:    Re: fc2, xorg, 2.6.x, scheduling latency peaks
From:       Fernando Pablo Lopez-Lezcano <nando () ccrma ! Stanford ! EDU>
Date:       2004-05-28 18:01:31
Message-ID: 1085767291.6347.23.camel () cmn37 ! stanford ! edu
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On Thu, 2004-05-27 at 22:58, Arjan van de Ven wrote:
> On Fri, 2004-05-28 at 02:39, Fernando Pablo Lopez-Lezcano wrote:
> > On Thu, 2004-05-27 at 17:25, Fernando Pablo Lopez-Lezcano wrote:
> > > Hi all. I'm trying to track the cause of high scheduling latency peaks
> > > in FC2 that make the system unusable for low latency audio work. 
> > > 
> > > Test systems: PIV laptop, radeon video chipset, AMD64 desktop, radeon
> > > video chipset. How I test: I run the Jack (Jack Audio Connection Kit)
> > > sound server with 2 or 3 128 frame buffers for low latency operation
> > > through the Qjackctl gui front-end. I then start GUI apps that use Jack
> > > (for example Freqtweak, Hydrogen and Jamin). I see plenty of buffer
> > > xruns of varying durations during the app load process and afterwards.
> > 
> > More data I forgot to include:
> > Jack is running with SCHED_FIFO priority. For achieving that I run a
> > custom kernel (currently based on Arjan's 1.391) with preempt enabled
> > and the realcap kernel module (by Jack O'Quin) added.
> 
> can you disable preempt? That should improve latencies....

I'll try that and report back. A while back - probably 2.6.4-1.279 or
whereabouts - I did a comparison (because of reports that it should be
better that preempt be off) and latencytest reported better latencies
with preempt on. Maybe something has changed since then (or I made some
silly mistake). 

-- Fernando



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