Poor SCSI performance for rawhide kernels

Mon Jul 30 14:23:40 UTC 2007

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?
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