On Thu, 20 Nov 2003, Mikael Johansson wrote:

Hello All!

Has anyone else experienced a drastic drop in read performance on software
RAID-0 with post 2.4.20 kernels? We have a few Athlon XP's here at our
lab with double IDE disks on different channels set up as RAID-0. Some
bonnie++ benchmark results with various kernels, on the same machine
(Athlon XP 2400+, 2 GHz, 1.5 GB RAM, VIA chipset, 2*Maxtor 120 GB
6Y060L0):
		write	read
2.4.20-ac1:	88,000 	135,000 K/sec
2.4.21-pre7:	93,000   75,000
2.4.22-ac4:	94,000	 82,000

So the write speed has gone up a bit, but the read speed performance has
plunged. Any ideas on what happened between 2.4.20 and 2.4.21 and what to
do about it? I'm eagerly awaiting suggestions, good read speed is quite
critical for many of our calculations :-) I will of course provide more
details if necessary.

There have been no significant changes in the RAID driver in 2.4.21, so I
suspect the cause for the slowdowns might the changes to the IO scheduler
(ll_rw_blk.c) or VM changes.

Isolating the -pre which the slowdown starts helps a lot.