Most of your performance of playing DVD's would be the rendering number
crunching inside your CPU.  The DMA is just helps the disk to memory
transport, which is nearly insignificant compared to the media decoding.

On my laptop, which the CPU speed is adjustable from 250MHz to 1000MHz, I
have found I need at least 500MHz on this PIII to watch a movie without
skipped frames.  250MHz is viewable, but slightly annoying.  Normally, DMA
is set to on by default since its more efficient, but since it is an ide
you can use /sbin/hdparm to tune hard drive performance.  The scsi-ide
driver is a thin layer and should not be an issue for performance.  Your
defaults should be similar to my DVD/CD-RW defaults:

[root@attaway dattaway]# hdparm /dev/hdc 

/dev/hdc:
 HDIO_GET_MULTCOUNT failed: Input/output error
 I/O support  =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 HDIO_GET_NOWERR failed: Input/output error
 readonly     =  0 (off)
 BLKRAGET failed: Input/output error
 HDIO_GETGEO_BIG failed: Invalid argument

[root@attaway dattaway]# hdparm -i /dev/hdc

/dev/hdc:

 Model=TOSHIBA DVD-ROM SD-R2002, FwRev=1W26, SerialNo=
 Config={ Fixed Removeable DTR<=5Mbs DTR>10Mbs nonMagnetic }
 RawCHS=0/0/0, TrkSize=0, SectSize=0, ECCbytes=0
 BuffType=unknown, BuffSize=2048kB, MaxMultSect=0
 (maybe): CurCHS=0/0/0, CurSects=0, LBA=yes, LBAsects=0
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes: pio0 pio1 pio2 pio3 pio4 
 DMA modes: mdma0 mdma1 *mdma2 
 AdvancedPM=no
 Drive Supports : ATA/ATAPI-5 T13 1321D revision 3 : ATA-2 ATA-3 ATA-4 
ATA-5 

I don't think there is too much tuning that can be done to the DVD, but I 
did find that the hard drive went from 4.9MB/sec to 20MB/sec with some 
minor tuning suggested by the hdparm manpage:

/sbin/hdparm -a16A1c1d1p4K1X69u1

I have used nvidia's proprietary drivers and xfree's vesa driver both with 
success.

Hope this helps!

On Fri, 1 Mar 2002, Lucas Peet wrote:

> Here's a good one for this list...
> 
> I have an LG DVD/CD-RW drive.  Works great - using scsi-ide module I can 
> burn CD's beautifully.  Thing is, I have a huge stack of DVD's I'd like 
> to watch as well.
> 
> I've installed Xine, and the d5d plugin, and my DVD's load & play. 
>  Performance is the issue here.  Everywhere I've seen, they say that you 
> should enable DMA access to the drive for peak performance, and playback 
> that's not choppy (which it is now).
> 
> X11:
> XFree86 Version 4.1.0 (Red Hat Linux release: 4.1.0-3) / X Window System
> Using latest NVidia drivers for TNT2
> 
> Any help by suggesting how I might be able to pull off DMA access & 
> scsi-ide for CD-RW would be super-helpful...(maybe pull the scsi-ide 
> module unless I'm burning CD's?  Would that work?)