Re: SSH GUI slow

On Mon, 12 May 2008 19:56:55 GMT curt <97WideGlide@xxxxxxxxxxxxxxx> wrote:
| On Mon, 12 May 2008 08:57:31 +0000, phil-news-nospam wrote:
|
|> On Fri, 09 May 2008 15:31:22 GMT curt <97WideGlide@xxxxxxxxxxxxxxx>
|> wrote:
|>
|> | I initially thought Matlab was the problem but I was very surprised to
|> | think that inefficient code can cause a GUI to run 10-15 times more |
|> slowly simply because it is being piped through ssh. I mean, nothing |
|> really changes except that the ssh tunnel is inserted into the equation,
|> | right ? The XWindow system is exactly the same, the hardware/driver |
|> configuration is exactly the same and the application is exactly the |
|> same. The only difference is the way these (and other) subsystems are |
|> working together via ssh.
|>
|> When it's not going through SSH, the difference between 1ms and 15ms to
|> update a window won't be noticed. This difference would be a function
|> how much data the application is sending through. In X, it can be a
|> lot. If it refreshes more window contents and not just the little bit
|> that changes, that volume of data can be a big load. SSH would have to
|> encrypt all of that data. Have you tried compression to see if it might
|> help?
|>
|>
|> | I've got to think that there is something else going on here.
|>
|> That's always possible. But I've used X over SSH before and found it
|> slow for some applications. It's not as bad as when I used X over a
|> dialup. In the case of dialup I could really see which apps were
|> problematic. For some, updates over dialup were in minutes, not seconds.
|
|
| It is not 1 milisecond versus 15 miliseconds. It is 2 seconds versus
| about 25 seconds which is very noticable. And it doesn't make any sense
| to me. Dialup, Highspeed, Cable, etc are not an issue. I am connecting
| to the same computer (client and server are the exact same machine). The
| only slowdown could be due to the logical networking within the machine.
| Where could this bottleneck be ?

SSH is always going to add some overhead. If without it the delay is already
2 seconds, then the application is overloading it, if that's on the same host.
Then adding encryption _and_ decryption to that (both on the same machine in
the case of localhost), the added delay does not surprise me since 2 seconds
is telling me there is an excess of data being sent.

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