[mythtv] mythmusic/cdparanoia question (a little OT).

Jim Radford mythtv-dev@snowman.net
Thu, 28 Nov 2002 08:44:36 -0800

On Thu, Nov 28, 2002 at 11:07:05AM -0500, Matt Zimmerman wrote:
> On Thu, Nov 28, 2002 at 07:47:53AM -0800, Jim Radford wrote:
> > On Wed, Nov 27, 2002 at 07:10:20PM -0500, Matt Zimmerman wrote:
> > > Welcome to the craptastic world of IDE.  I have a 40x IDE CD-ROM and a 32X
> > > SCSI CD-RW in this machine.  While the IDE drive does CDDA slightly faster,
> > > it uses about 1000% more CPU than the SCSI drive.

> > Nope, that's just linux that's crappy (inspired by the initially
> > crappy IDE cdroms) as it uses PIO instead of DMA when talking to the
> > cdrom.  The newer 2.5 kernels don't have this problem thanks to Jens
> > Axboe.

> This sounds great...but why do I see a similar (though less drastic)
> difference between IDE and SCSI CPU utilization for hard disks, even when
> DMA is enabled?

I can think of lots of reasons like average transfer size (smaller
transfers mean more setup by the CPU) or hardware scatter gather
support (multiple small transfers with little CPU interaction), but
none are fundamental differences between IDE and SCSI, rather
differences in the controllers and drivers you have.