I've been playing around today a lot with sysbench, and observed that 2.6.32 kernel supplied by Ubuntu is having perf regression with PG (which does not affect MySQL), compared to 2.6.28 builds I have.
What I observed can be seen in a paste at http://p.defau.lt/?8_GQV82Pz3_SDZbNOdP93Q (db12 is 2.6.28, db20 is 2.6.32 - 2.6.32-24-server).
Machines are two socket quad-opterons 2356s.
oprofile output can be seen at http://p.defau.lt/?OIR1vDFK4cze_fmBTQbV9w - system has >20% of idle cpu, which is somewhere in the top symbol :)
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