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SubjectRe: 2.6.4-mm2
Sorry I'm falling behind...  I see about a 10% decrease in throughput
with our dbt2 workload when comparing 2.6.4-mm2 to 2.6.3. I'm wondering
if this might be a result of the changes to the pagecache, radix-tree
and writeback code since you mentioned it could affect i/o scheduling in
2.6.4-mm1.

PostgreSQL is using 8KB blocks and the characteristics of the i/o should
be that one lvm2 volume is experiencing mostly sequential writes, while
another has random reading and writing. Both these volumes are using
ext2. I'll summarize the throughput results here, with the lvm2 stripe
width varying across the columns:

kernel 16 kb 32 kb 64 kb 128 kb 256 kb 512 kb
2.6.3 2308 2335 2348 2334
2.6.4-mm2 2028 2048 2074 2096 2082 2078

Here's a page with links to profile, oprofile, etc of each result:
http://developer.osdl.org/markw/linux/2.6-pagecache.html

Comparing one pair of readprofile results, I find it curious that
dm_table_unplug_all and dm_table_any_congested show up near the top of a
2.6.4-mm2 profile when they haven't shown up before in 2.6.3.

Mark
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