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Date: Fri, 24 Dec 2004 21:11:36 -0600 (CST)
From: Mike Silbersack <silby@silby.com>
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Subject: Disk access SOLVES sound stutter!
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My laptop has built-in sound:

pcm0: <Acer Labs M5451> port 0x1000-0x10ff mem 0xd0001000-0xd0001fff irq 5 
at device 6.0 on pci0
pcm0: <Conexant CX20468 AC97 Codec>
pcm0: [GIANT-LOCKED]

I haven't played with it much, but I started doing so again recently.  The 
sound quality is rather poor when the system is idle, it sounds as if it's 
playing too slowly.

However, while there is disk activity going on (start Konqueror, OO, 
opening my huge inbox, etc), the sound is perfect.  systat -vm shows this 
to be due to interrupt rates.  Although irq 5 is not shared with anything 
else, disk activity causes the interrupt rate for irq 5 to increase from 
~79 per second to ~84 per second.

This is a 6.0-current UP system.  4BSD scheduler, preemption enabled.

Any clue as to why this might be happening?  Sounds like something very 
interesting going on in some low level system somewhere. :)

BTW, mpg123 and xmms were both used for testing, with and without X 
running; results always seem to fix the above profile.

Mike "Silby" Silbersack