Poor SCSI performance for rawhide kernels

[orion at cora.nwra.com]

> While debugging an issue with the aic7xxx driver, I noticed that SCSI
> performance is quite poor for the current development kernel compared to
> release kernels.
> For a U160 disk attached to a 2940UW controller, FAST-20 mode [which, btw,
> has to be forced manually, see
> https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=171282] delivers more
> than 28 MB/s [hdparm -t /dev/sda] for the latest F7 update kernel
> 2.6.22.1-33.fc7 [compared to the nominal rate of 40 MB/s] whereas it drops
> by almost 30% to about 20 MB/s for rawhide kernel 2.6.23-0.49.rc1.git3.fc8
> which is barely more than in FAST-10 mode. It this difference of the order
> one would expect?

I've seen similar results before which I attributed to the added debugging
turned on in the rawhide kernels.

- orion