Subject: Re: UVM/other problems for desktop users in current?
To: Daniel Carosone <firstname.lastname@example.org>
From: Jukka Marin <email@example.com>
Date: 12/18/2002 09:37:52
On Wed, Dec 18, 2002 at 06:33:27PM +1100, Daniel Carosone wrote:
> On Wed, Dec 18, 2002 at 09:23:32AM +0200, Jukka Marin wrote:
> > Yep. And I'd appreciate it if someone explained _why_ decent IDE with DMA
> > is so bad when compared to SCSI. Especially if you only have one device
> > per port and the raw sustained performance is 30 MB/s or more with only a
> > little CPU loading.
> The main reason is that there's only one outstanding operation to
> the disk at once. SCSI disks, with tagged queueing, allow multiple
> outstanding requests, that the drive can respond to in the order
> that best suits its internal state (disk head position, mostly).
But with the large RAM caches on the disk (like 8 MB in my case), can't
the disk still do the actual (write) operations in an optimized order?
Well, 8 MB may not be as good as a long command queue..