2.6.x scsi software raid IO tuning

[Richard Smith <rsmith@bitworks.com>]

I receintly came across several SCSI racks with drives.  So I've been
playing with various software RAID setups with between 8 - 15 drives. I
have a sym8xx SE chain and a AIC7xxx HVD chain.  Using Bonnie++ to
measure IO throughput of my RAID 5 setup.

I also decided to try the latest 2.6 test kernels.  I built the 2.6 with
the same setup as my 2.4.22 kernel.  Preemption was disabled and I
believe that I have all debugging output turned off.

I found that in every test case I ran Bonnie++ reported the 2.6 kernel
IO as 3 to 5 MB/s slower than the 2.4 kernel.  File creation/deletion 
was also slower.

Is there some tuning knobs that I need to tweak or some option that
might be enabled causing this?  I thought the 2.6 was supposed to have
much better IO throughput when setup in non-preempt.  So I expected to
at least get the same numbers not less.

My apologies if this is a md issue rather than a scsi issue but out of 
my info searches so far this list seemed like the best place to ask for 
info.

-- 
Richard A. Smith
rsmith@bitworks.com