Re: HEADS UP: More CAM fixes.

On Tue, 17 Feb 2009 13:46:20 -0700
Scott Long <scottl_at_samsco.org> wrote:

> 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
> 

Maybe I misunderstood something, but I thought the patch was supposed
to improve queuing.  Seems like all the seeks during a buildowrld
would exercise that.  All I can say is that the disk did _lots_ of
seeking.

---
Gary Jennejohn