interactive shell very slow
I have a problem with our servers every once in awhile. They are red hat 4. This particular case, the server has 2x dual core Opteron processors and 26 gb of RAM and I've dug around, without finding a cause. Very odd.
The ssh shell performance is horrible. Just doing an ls of one file is very slow. About 1.5 seconds when it should be about .002 seconds. The disk IO is non existent according to sar and top. Anyone have ideas? uname: Code:
2.6.9-34.ELsmp #1 SMP Fri Feb 24 16:56:28 EST 2006 x86_64 x86_64 x86_64 GNU/Linux Code:
top - 23:19:51 up 3 days, 10:57, 2 users, load average: 1.61, 1.60, 1.69 |
Did you try telnet? Or ftp? Something unencrypted and character-based.
For ftp, check if ls is also slow and then check a transfer. Could be network related, or host related (encryption layer, general problem..) |
Same problems on the actual console as an ssh shell.
Notice top is at 48% which isn't right. |
It's not using any swap.. very unusual. Normally Linux always has a small amt of RAM free (as here) and a small amt of swap used. Zero swap used is practically unheard of.
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infinity005, have you physical access or only network access? edit: oops I just see this: 9496 bhsu 30 5 5119m 4.8g 38m R 99.9 20.5 4337:51 mantle That's a lot of memory!! Mem: 24751368k total, 24703604k used, 47764k free, 702860k buffers eeek! 24Gb! That's also some memory!! Should be fine without swap. Can you stop this process for a moment? |
The process completed and the system responds normally again.
We have another similar machine that was running mantle with no performance issues. ...why when this system runs mantle and the interactive performance as well as processes using a strange amount of CPU is beyond me at this point. |
Is there any additional debugging that I can enable somewhere?
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The thing is 24G is lots of RAM, but 47M free is tiny by comparison and zero swap is not right. Even when a Unix/Linux system is just ticking over it always uses a small amt of swap, prob just for bookkeeping purposes (ie so it knows where swap has got to).
As soon as a prog on that box tries to use some more RAM, it's burn that 47M real fast and slow down. Unix/Linux needs some free RAM at all times to move processes/data around eg into/out of the cpu (run list) |
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Another server: Code:
top - 22:22:44 up 52 days, 7:51, 10 users, load average: 1.94, 1.88, 1.81 Code:
top - 16:21:52 up 4:20, 5 users, load average: 0.00, 0.00, 0.00 |
Mem: 24751368k total, 24703604k used, 47764k free, 702860k buffers
You have 47M free but 702M buffered. So you really have 749M free from what I see. Depending on swapiness, it will prefer to use the buffer rather than swap on disk. When buffers drop under a certain level as free then it should use the swap. |
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server@talkie:~$ free |
Well, that's very interesting. I've never seen a server that had absolutely zero swap used and zero load avgs. As I say, normally just basic background activity generates some numbers....
You learn something everyday... If anyone is interested in how load avg is calc and what it really means, here is a good 2 part article: http://www.teamquest.com/resources/g...ay/5/index.htm |
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