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number_nine
Tux's lil' helper
Joined: 05 May 2005
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 Posted: Wed Aug 29, 2007 7:19 pm Post subject: ssh X11 cpu load problems |
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Five people (including myself) all log into one of our servers via ssh and run the same X11 application (using X forwarding). We all have Windows boxes, but the server is Linux. We are using Cygwin to establish the ssh connection as well as host the X11 display.
One colleague and myself cause the CPU load on the server and our local machines to go up considerably. Using top on the server shows that our respective ssh processes are taking the CPU. Same goes for Windows Task Manager on our PCs. If we kill the X11 application, the load immediately goes away.
Does anyone have any idea why two of us would have these performance/CPU load problems, compared to the other three (who do the exact same thing and don't have this problem)?
My first thought was that we have different ssh versions, and some default option was changed which causes higher CPU load. But I can't seem to figure out what this is. A non-CPU load inducing machine is running this: OpenSSH_4.3p2, OpenSSL 0.9.8b 04 May 2006. I have this: OpenSSH_4.6p1, OpenSSL 0.9.8e 23 Feb 2007.
Thoughts?
Thanks! |
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barophobia
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| Posted: Wed Aug 29, 2007 9:50 pm Post subject: |
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No gpu acceleration for x11 forwards so everything that is drawn goes through the cpu.
This really sucks when using a opengl app. The more often the app redraws the screen you will notice more cpu usage on both sides.
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Hu
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| Posted: Thu Aug 30, 2007 3:17 am Post subject: |
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| Does the X11 application support any per-user configuration? Perhaps the users who do not cause a load have their instance configured in a way which requires less CPU when it displays. |
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number_nine
Tux's lil' helper
Joined: 05 May 2005
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| Posted: Thu Aug 30, 2007 12:30 pm Post subject: |
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| barophobia wrote: | No gpu acceleration for x11 forwards so everything that is drawn goes through the cpu.
This really sucks when using a opengl app. The more often the app redraws the screen you will notice more cpu usage on both sides. |
If that's the case, why would it only affect two of the five us us? Ironically, the two of us with the problems have the newest/fastest machines.
| Hu wrote: | | Does the X11 application support any per-user configuration? Perhaps the users who do not cause a load have their instance configured in a way which requires less CPU when it displays. |
Nope, the application is just a generic monitoring application. No per-user config, everyone sees the same thing. |
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JeliJami
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| Posted: Thu Aug 30, 2007 3:55 pm Post subject: |
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Do you use the same options to connect?
- compression on/off
- encryption: AES, 3DES, Blowfish, CAST128, or Arcfour (man ssh)
- port forwarding
- ...
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number_nine
Tux's lil' helper
Joined: 05 May 2005
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| Posted: Thu Aug 30, 2007 4:15 pm Post subject: |
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| davjel wrote: | Do you use the same options to connect?
- compression on/off
- encryption: AES, 3DES, Blowfish, CAST128, or Arcfour (man ssh)
- port forwarding
- ... |
The same explicit options were used, but the I'm wondering if the implicit defaults changed (in OpenSSH/OpenSSL versions)?
Is there a way to get a dump of all runtime config options from ssh?
Thanks again! |
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barophobia
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| Posted: Thu Aug 30, 2007 4:28 pm Post subject: |
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| number_nine wrote: |
If that's the case, why would it only affect two of the five us us? Ironically, the two of us with the problems have the newest/fastest machines.
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So then I assume you all are running the same app? with the same usage patterns?
Then I don't know maybe something is forcing a more frequent redraw?
Compression and encryption algorithm should have almost no effect assuming you are on a local lan.
debug option for ssh is -vvv one to three v's
Be nice to your computer and the computer will be nice to you.
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number_nine
Tux's lil' helper
Joined: 05 May 2005
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| Posted: Thu Aug 30, 2007 5:55 pm Post subject: |
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| barophobia wrote: | | number_nine wrote: |
If that's the case, why would it only affect two of the five us us? Ironically, the two of us with the problems have the newest/fastest machines.
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So then I assume you all are running the same app? with the same usage patterns?
Then I don't know maybe something is forcing a more frequent redraw?
Compression and encryption algorithm should have almost no effect assuming you are on a local lan.
debug option for ssh is -vvv one to three v's |
Yes, we are all running the same app, definitely with the same usage patterns (it's just a monitoring app, so it's only real "use" is to look at it).
Regarding the more frequent redraw: if I minimize the application, the CPU load remains. Wouldn't minimizing it remove the need to constantly redraw/repaint?
We are all on the same local LAN.
I ran my ssh session with -v -v -v and my colleague (whose instance does not result in high CPU load) did the same. Both outputs were piped to a file. The two resulting files were virtually the same, as far as I could tell.
That's why I was hoping I could run ssh with some command that would just list every configurable runtime parameter and its value.
Anyway, thanks for the ideas and help! |
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barophobia
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| Posted: Fri Aug 31, 2007 5:08 am Post subject: |
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| number_nine wrote: |
Regarding the more frequent redraw: if I minimize the application, the CPU load remains. Wouldn't minimizing it remove the need to constantly redraw/repaint?
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Only if the programmer is being smart. Won't bet my life on it.
I have no clue why this is happening to you, other than the computer just doesn't like you.
Well I don't do tech support or sys. admin. for a reason. =P good luck.
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