frustratingly slow box at 4GB, but not 1GB of memory
From: Adrian Filipi (adrian+freebsd-perf_at_ubergeeks.com)
Date: 02/03/04
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Date: Tue, 3 Feb 2004 12:26:19 -0500 (EST) To: freebsd-performance@freebsd.org
Hi folks,
I've got a box I'm helping tune and it's not really responding as
I'd expect.
It's a dual 2GHz Xeon box running on a Supermicro P4DLR motherboard
with 4GB of physical RAM. It has 4GB of swap configured on a hardware
RAID5 configuration.
It's running 4.9-RELEASE. It's also running Apache with PHP and
Perl CGI's. The CGI's read/write to a MySQL DB.
Briefly, it responds pretty quickly when I only let the kernel use
1GB of the RAM, but gets bogged down when I let it use the full 4GB. I'm
limiting the RAM by setting hw.physmem.
I've tried some of the things that I could dig up in the archives,
but the knowledge is pretty widely scattered. :-(
I have MAXUSERS set to 96 as that gets me plenty of file
descriptors and pid's. While tight, I believe I could get away with only
32, as there should not be more than 300-400 processes running at any one
time.
I set vm.pmap.shpgperproc="300" because of warnings from the
kernel. I'm not sure if this is the best value, but it made the warnings
go away.
First, upping the KVA_PAGES to 768 to achieve a 3:1 ration of
kernel to user memory, didn't change things.
Disabling swap seems to make a huge difference. It changes the
time results for "time top -bu" by two orders of magnitude from 0.006s to
0.6s! In fact, I can run the box reasonably well with 2GB of RAM with swap
disabled.
If I let the box boot using all of the RAM, it is very slow. e.g.
"time top -bu >/dev/null" takes about 6 seconds.
I am seeing large runs of time (15-30 seconds) where the system
time usage is in the high range (75-99). Does anyone have a suggestion on
how to determine which kernel data structures are the problems?
thanks,
Adrian
-- [ adrian@ubergeeks.com ] _______________________________________________ freebsd-performance@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-performance To unsubscribe, send any mail to "freebsd-performance-unsubscribe@freebsd.org"
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