performance degradation in 6.2 when adding a second quad core chip
bthielsen at safarivideonetworks.com
Thu Feb 21 22:39:37 UTC 2008
we've been experiencing some interesting behavior on single quad core
computers as compared to dual quad core computers.
it appears that adding a second processor to the system (leaving it
otherwise untouched) actually decreases performance. we've got a
small rudimentary test process, built in house, that does postgresql
queries (selects) via http requests (apache2/php5).
here is a small data set from what we've seen so far:
a user is one iteration of a curl statement and values listed in the
cpu columns are average time before the page returns, in seconds.
users 1 cpu 2 cpu
60 2.48 2.18
80 3.34 2.72
100 4.18 5.34
120 9.48 15.61
140 13.2 46.16
160 26.28 66.99
we're confident that nothing else has changed other than the addition
of the chip, so i'm hoping for some insight on where we might look for
clues. the above results used 6.2-RELEASE. we've started the same
test using 7.0-RC2 and are seeing similar response times with both
processors in place. next on our list is doing a single processor
iteration of the 7.0-RC2 test to corroborate that data, followed by a
local test to query pg more directly, removing apache and friends from
the equation, in hopes of getting some clarity.
below are the basics of this configuration - this is a new list for
me, so i've been conservative, but i'm happy to provide as much detail
as is helpful.
dell poweredge 2900
xeon quad core 2 ghz / 1333 mhz bus speed / 2 x 6mb l2 cache
4 gb 667 mhz memory
all of the software has been installed via ports, the 6.2 kernel is a
custom kernel with (i believe) mostly rudimentary changes and support
for the perc6 disk controller (that became available in 7) added, and
the 7.0 kernel contains the same changes as the 6.2 kernel, excluding
the custom perc6 support.
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