HEADS UP: More CAM fixes.

[Scott Long]

Bruce Evans wrote:
> 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

Yes, on modern machines, buildworld is bound almost completely by disk
latency, and not at all by disk or controller bandwidth.

Scott