dump time increase by 1h with new kernel

[I got no response on -general for a few days so I'm trying here]

When we upgraded from linux-2.6.24 to linux-2.6.27, our pg_dump
duration increased by 20% from 5 hours to 6.  My first attempt at
resolution was to boot with elevator=deadline.  However that's
actually the default IO scheduler in both kernels.

The two dmesg's are at:
https://www.norchemlab.com/tmp/linux-2.6.24-22.45-server
https://www.norchemlab.com/tmp/linux-2.6.27-14.41-server

The database partition is: xfs / lvm / aic79xx / scsi.

Booting back into the .24 kernel brings the pg_dump back down to 5
hours (for daily 20GB output compressed by pg_dump -Fc).

Does anyone know what might be different which could cause such a
drastic change?

Thanks,
Justin