Re: [linux-audio-dev] (not so low) low latency - acpi, dri, proc

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Subject: Re: [linux-audio-dev] (not so low) low latency - acpi, dri, proc
From: Joern Nettingsmeier (nettings_AT_folkwang-hochschule.de)
Date: Sat Aug 24 2002 - 00:57:09 EEST

as a related note, i have found the soft-raid driver to cause higher
latencies.
when i do latencytest on a single scsi drive, i'm always <3ms, on the
raid, i sometimes see 10.
kernel is 2.4.20-pre2-ll. this data is as i recall it. if folks are
interested, i'll make the graphs available.

Fernando Pablo Lopez-Lezcano wrote:
>
> Hi... anybody out there testing latency on an ACPI patched
> kernel? I have two kernels I'm testing:
>
> 2.4.19-x:
> 2.4.19
> 2.4.20-pre4
> low latency for 2.4.19 (w/a couple of tweaks to patch pre4)
> acpi-20020815 for 2.4.20-pre4
>
> 2.4.18-x:
> 2.4.18
> low latency for 2.4.18-pre10
> acpi-20020726 for 2.4.18
>
> On both 2.4.18-x and 2.4.19-x I get quite high periodic
> latency peaks that hover around 170mSecs.
>
> I suspect acpi might be the culprit but I cannot try to
> disable it because on this particular laptop you need acpi to
> make sound work (probably something to do with routing of
> interrupts,, also tried pci=biosirq on a non-acpi kernel
> without success). Any suggestions?
>
> DRI: I was about to write something about this and then
> checked and yes, the latest lowlat patch (for 2.4.19) is
> missing the dri reschedules (from Jussi Lako's patch set) so
> that DRI is unusable if you don't add them (at least on a
> Radeon based laptop). I'm recompiling with them to do more
> tests.
>
> Proc: something has changed from the 2.4.18 to the 2.4.19
> kernels (maybe the acpi proc interface is to blame?). Big
> mess of latency spikes in the proc latency test.
>
> I'll post latency graphs later... this is all using
> latencytest 0.42
>
> -- Fernando 

-- 
Jörn Nettingsmeier     
Kurfürstenstr 49, 45138 Essen, Germany      
http://spunk.dnsalias.org (my server)
http://www.linuxdj.com/audio/lad/ (Linux Audio Developers)

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