read blocking for really long time on /dev/scd?

I'm having a problem with ogle glitching. It seems what's happening is it isn't able to read data from the dvd fast enough to feed the decoder. Sometimes read system calls block for seconds at a time. That doesn't seem normal.

In the following straces fd 3 is /dev/scd1. I'm using an ide dvd-rom with ide-scsi. DMA is enabled on the ide device.

Most read calls return in about 26us. But a significant chunk seem to take up to 150ms to return. Those slow reads don't cause ogle any problem but they seem to indicate a problem already. But every now and then a read will hang for a really long time, I've seen as much as 10s.

Here's an example that was correlated with a glitch in video playback:

read(3, "\0\0\1\272D\0-C6E\1\211\303\370\0\0\1\340\7\354\221\300"..., 288768) = 288768 <2.747268>

My question is I guess: Do other people observe the same issue? Is it expected? What is the path from the read syscall through the ide-scsi layer to the ide driver that the read syscall is waiting on? How do I go about tracking down where in the scd or atapi ide driver this hang is happening?

Background info:

This is a custom build from pristine source from linux.kernel.org:

bash-2.05b# uname -a
Linux stark.dyndns.tv 2.4.19 #6 Tue Sep 10 22:08:51 EDT 2002 i686 unknown unknown GNU/Linux

bash-2.05b# hdparm /dev/hdd
/dev/hdd:
HDIO_GET_MULTCOUNT failed: Input/output error

 IO_support   =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 readonly     =  0 (off)

BLKRAGET failed: Input/output error
HDIO_GETGEO failed: Invalid argument

bash-2.05b# hdparm -i /dev/hdd
/dev/hdd:

Model=LG DVD-ROM DRD-8160B, FwRev=1.01, SerialNo= Config={ Fixed Removeable DTR<=5Mbs DTR>10Mbs nonMagnetic } RawCHS=0/0/0, TrkSize=0, SectSize=0, ECCbytes=0 BuffType=unknown, BuffSize=0kB, MaxMultSect=0
(maybe): CurCHS=0/0/0, CurSects=0, LBA=yes, LBAsects=0 IORDY=on/off, tPIO={min:227,w/IORDY:120}, tDMA={min:120,rec:150} PIO modes: pio0 pio1 pio2 pio3 pio4
DMA modes: sdma0 sdma1 sdma2 mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 *udma2
AdvancedPM=no

Here are the modules loaded, however I have tested this problem with a fresh reboot with hardly any of these modules loaded and the problem definitely still occurs. I had openafs, pcmcia, parport, mga, agpgar, pppoe all unloaded.

bash-2.05b# lsmod
Module Size Used by Tainted: PF

sr_mod                 12304   4  (autoclean)
openafs               403712   2 
pcmcia_core            39872   0 
serial                 50884   0  (autoclean)
isa-pnp                28708   0  (autoclean) [serial]
parport_pc             25288   1  (autoclean)
lp                      6432   0  (autoclean)
parport                25024   1  (autoclean) [parport_pc lp]
mga_vid                 7800   0 
mga                    98104   3 
agpgart                16552   3 
ide-scsi                7632   2 
scsi_mod               51356   2  [sr_mod ide-scsi]
pppoe                   6924   2 
pppox                   1128   1  [pppoe]
ppp_generic            16416   3  [pppoe pppox]
slhc                    4480   0  [ppp_generic]
ne2k-pci                4800   1 
8390                    5968   0  [ne2k-pci]
rtc                     5916   0  (autoclean)

greg