Linux 2.2 vs 2.4

Hi,

Not sure if anyone will find this of interest, but I ran
pgbench on my main Linux box to see what sort of performance
difference might be visible between 2.2 and 2.4 kernels.

Hardware: A dual P3-450 with 384Mb of RAM and 3 SCSI disks.
The pg datafiles live in a half-gig partition on the first
one.

Software: Red Hat 6.1 plus all sort of bits and pieces.
PostgreSQL 7.1beta4 RPMs. pgbench hand-compiled from source
for same. No options changed from defaults. (I'll look at
that tomorrow -- is there anything worth changing other than
commit_delay and fsync?)

Kernels: 2.2.15 + software RAID patches, 2.4.2-pre2

With 2.2.15:
pgbench -s5 -i: 1.27.78 elapsed
pgbench -s5 -t100:
clients: TPS / TPS (excluding connection establishment)
1: 39.66 / 40.08 TPS
2: 60.77 / 61.64 TPS
4: 76.15 / 77.42
8: 90.99 / 92.73
16: 71.10 / 72.15
32: 49.20 / 49.70
1: 27.76 / 28.00
1: 27.82 / 28.03

pgbench -v -s5 -t100:
1: 30.73 / 30.98

And with 2.4.2-pre2:
pgbench -s5 -i: 1:17.46 elapsed
pgbench -s5 -t100
1: 43.57 / 44.11 TPS
2: 62.85 / 63.86 TPS
4: 87.24 / 89.08 TPS
8: 86.60 / 88.38 TPS
16: 53.22 / 53.88 TPS
32: 60.28 / 61.10 TPS
1: 35.93 / 36.33
1: 34.82 / 35.18

pgbench -v -s5 -t100:
1: 35.70 / 36.01

Overall, two things jump out at me.

Firstly, it looks like 2.4 is mixed news for heavy pgbench users
:) Low-utilisation numbers are better, but the sweet spot seems
lower and narrower.

Secondly, in both occasions after a run, performance has been
more than 20% lower. Restarting or performing a full vacuum does
not seem to help. Is there some sort of fragmentation issue
here?

Matthew.