Odd speed problems with aic79xx drivers on RHEL

[LKML]

We have a Dual Xeon server with onboard aic79xx based controller, which is
connected to a 16port SATA-SCSI RAID unit, which supports Ultra160.

When we first got the server, it was running RH9 with a custom kernel, and
we were getting bonnie++ test results of 100MB/s read and write speed on
the custom 2.4.21 based kernel(with aic79xx driver 1.3.x) while keeping a
load average of approximatel 1.7.

Once we installed Redhat Enterprise Linux AS 3.0, with its 2.4.21-4.EL
kernel, we've been getting write speed of 120MB/s, but read speed of only
about 50MB/s.  That's right, read is slower than write.  I've tried upping
the TCQ from the default of 32 to 253, and that decreased the read speed
even further, down to 40MB/s.

We've tried putting back on the server vendor's custom kernel, but that
kernel now seg faults whenever we run bonnie++.

I've tried recomping the Enterprise kernel with the latest aic79xx driver
from Justin's site, with no change.  Turning TCQ turned off, I was able to
get 95MB/s read and write, but at a much higher load average of 2.9.
Shouldn't enabling TCQ improve the speed?  Any thoughts or suggestions on
what to try next?

- John

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