Re: Strange behavior: pgbench and new Linux kernels

On Thu, 17 Apr 2008, Matthew wrote:

> The last message in the thread says that 2.6.25-rc6 has the problem nailed.
> That was a month ago. So I guess, upgrade to 2.6.25, which was released
> today.

Ah, even more support for me to distrust everything I read. The change
has flattened out things, so now the pgbench results are awful everywhere.
On this benchmark 2.6.25 is the worst kernel yet:

-bash-3.00$ pgbench -S -c 4 -t 10000 pgbench | grep excluding
tps = 8619.710649 (excluding connections establishing)
tps = 8664.321235 (excluding connections establishing)
tps = 8671.973915 (excluding connections establishing)
(was 18388 in 2.6.9 and 16621 in 2.6.23-3)

-bash-3.00$ pgbench -S -c 8 -t 10000 pgbench | grep excluding
tps = 9011.728765 (excluding connections establishing)
tps = 9039.441796 (excluding connections establishing)
tps = 9206.574000 (excluding connections establishing)
(was 15760 in 2.6.9 and 15551 in 2.6.23-3)

-bash-3.00$ pgbench -S -c 16 -t 10000 pgbench | grep excluding
tps = 7063.710786 (excluding connections establishing)
tps = 6956.266777 (excluding connections establishing)
tps = 7120.971600 (excluding connections establishing)
(was 14148 in 2.6.9 and 7311 in 2.6.23-3)

-bash-3.00$ pgbench -S -c 32 -t 10000 pgbench | grep excluding
tps = 7006.311636 (excluding connections establishing)
tps = 6971.305909 (excluding connections establishing)
tps = 7002.820583 (excluding connections establishing)
(was 13647 in 2.6.9 and 7141 in 2.6.23-3)

This is what happens when the kernel developers are using results from a
MySQL tool to optimize things I guess. It seems I have a lot of work
ahead of me here to nail down and report what's going on here.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD