HEADS UP: More CAM fixes.

[Bruce Evans]

On Tue, 17 Feb 2009, Gary Jennejohn wrote:

> I tested this with an Adaptec 29160.  I saw no real improvement in
> performance, but also no regressions.
>
> I suspect that the old disk I had attached just didn't have enough
> performance reserves to show an improvement.
>
> My test scenario was buildworld.  Since /usr/src and /usr/obj were both
> on the one disk it got a pretty good workout.
                                   ^^^^ low
>
> AMD64 X2 (2.5 GHz) with 4GB of RAM.

Buildworld hardly uses the disk at all.  It reads and writes a few hundred
MB.  Ideally the i/o should go at disk speeds of 50-200MB/S and thus take
between 20 and 5 seconds.  In practice, it will take a few more seconds.
physically but perhaps even less virtually due to parallelism.

Bruce