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The video was not very smooth (minor stop/start every few seconds) using xine or ogle to watch a DVD. Ripping the VOBs to disk and watching that was just fine. Hence the problem was tracked to extracting from the DVD. Tuning seemed to fix it:

$ hdparm /dev/hdc /dev/hdc: HDIO_GET_MULTCOUNT failed: Invalid argument IO_support = 0 (default 16-bit) unmaskirq = 0 (off) using_dma = 0 (off) keepsettings = 0 (off) readonly = 0 (off) readahead = 256 (on) HDIO_GETGEO failed: Invalid argument

From http://www.mplayerhq.hu/DOCS/HTML/en/drives.html some tuning was suggested. The suggestion included turning DMA on, but that failed:

$ sudo hdparm -d1 -a8 -u1 /dev/hdc /dev/hdc: setting fs readahead to 8 setting unmaskirq to 1 (on) setting using_dma to 1 (on) HDIO_SET_DMA failed: Operation not permitted unmaskirq = 1 (on) using_dma = 0 (off) readahead = 8 (on)

The resulting DVD watching is smooth. A little experimenting indicates that the -a8 did the trick. Place this into /etc/init.d/hwtools to have it survive a reboot.

Note that according to the Red Hat Linux Release Notes (http://www.redhat.com/docs/manuals/linux/RHL-8.0-Manual/release-notes/x86/) DMA is often disabled on CD-ROM drives because they are often not capable of IDE DMA. If you are sure that your CD-ROM drive is capable of IDE DMA you can do the following:

# rmmod ide_cd # modprobe ide-cd dma=1

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