Andrew Morton wrote:
It could be due to I/O scheduler changes. Which one are you using? CFQ?
Or it could be that there has been some changed behaviour at the VFS/pagecache
layer: the VFS might be submitting little hunks of lots of files, rather than
large hunks of few files.
Or it could be a block-layer thing: perhaps some driver change has caused
us to be placing less data into the queue. Which device driver is that machine
using?
Being a simple soul, the first thing I'll try when I get near a test box
will be
for i in $(seq 1 16)
do
time dd if=/dev/zero of=$i bs=1M count=1024 &
done
I tried first the test with dd, the results are similar to those of FFSB
tests, about 15 percent of degradation between 2.6.20.7 and 2.6.21-rc7.
I'm using the CFQ I/O scheduler. I changed it to the "deadline" one and
I don't have any more the problem, I've got similar throughput values
with 2.6.20.7 and 2.6.21-rc7 kernels.
So can we conclude that it's due to the CFQ scheduler?
I also checked the device driver used, the revision number is the same
in 2.6.20 and 2.6.21.
Valérie
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