Remote X: bad performance

[Bartman]

I was experimenting a bit with running remote X apps. This is what I did:

From my local computer at home, I set up ssh connection to remote computer (at university), and forward X connection. Then start remote X apps over that ssh line.

The problem is that the bandwidth was pretty low (about 64 kbits/s). I often connect that server with http, ftp, mail,... and I easily get connection speeds of 2 Mbits/s. Also, the ping is about 25 ms.

So, what could cause this bad performance with X? Is there some sort of benchmark I can run to see what the problem could be?

[redhead]

Every thing transfered between the two machines is encrypted on the server, send to your machine then decrypted, and shown to you.
Even the contence of the x-app, what it should look like, etc..
So in this matter the CPU-power of the two will have an effect aswell.

If it's browsing, then the transfere will be like:

- you click a link in the browser started from the server.
- your machine encrypts the fact that the app should have a mouse click at possition(x,y)
- server decrypts the possition, sends it to the x-app.
- the x-app enterprets it to follow the link and tells the server to fetch the new page.
- The server fetches the page, and tells the x-app to show it.
- The x-app wants to show it, so it tells the server to encrypt the contence, and send it to you.
- The server sends the page-contence encrypted to your machine.
- Your machine decrypts the contence and displays it for you.

Kinda a long way for just the contence of some HTML code..

[Bartman]

Some points:

a) ssh encryption uses DES, which is very fast and doesnt cause too much overhead.
b) Everything you describe also happens when running local apps, so why should it suddenly be a problem?
c) CPU power doesnt seem to be a problem, top reports 86% idle time local and 94% idle time remote.

I have really no idea what causes the slowdown.

[Schotty]

Can you do it across your LAN at acceptable speeds? If not, then there is something wrong. I knw a guy that did that on a 28.8K modem all day three days a week. He telecommuted from his home in Milwaukee to San Deigo. He was the one who told me first about remote X over SSH. So, if your LAN (100Mbit or 10Mbit) is unable to handle what 28.8Kbit (notice we are talking %10 of the bandwidth) could do fine, there is another issue at hand.

[Bartman]

Schotty: dont have a LAN, so thats not really an option

For the guy with the modem, it could be that he ran only graphics-extensive apps. I'm thinking about running intensive software, which runs faster on the server at university. I know because they also have public X terminals and there things go really fast

Anyone knows of X benchmarks? That could make some things clear.

[Schotty]

Well, I am slightly confused... If you are doing a remote X session, the server will always run the app. So If you want to do work at school on your dorm/apartment/home PC, the apps that pop up on the XTerm will actually be run on your remote box. IF you are really lucky, you can find a way to get access to the schools' X Server(s) and do work from home on there. Thats a dirty way to increase your SETI/genome@home scores

Do realize the direction the most data has to flow. You may be SOL no matter wht you do - if there are alot of ethernet SWITCHES, you may be lagging your connection down to an inhumane level.

[Bartman]

[quote author=GOP Schotty link=board=6;threadid=4957;start=0#49601 date=1032203629]
Well, I am slightly confused... If you are doing a remote X session, the server will always run the app. So If you want to do work at school on your dorm/apartment/home PC, the apps that pop up on the XTerm will actually be run on your remote box. IF you are really lucky, you can find a way to get access to the schools' X Server(s) and do work from home on there. Thats a dirty way to increase your SETI/genome@home scores

Do realize the direction the most data has to flow. You may be SOL no matter wht you do - if there are alot of ethernet SWITCHES, you may be lagging your connection down to an inhumane level.
[/quote]

Allright, let me see what you mean with this...
Running apps on the remote box is what I want. I ssh -X my home computer to the remote host at school, and then run apps on the remote end, which display at home. Right?

But the question remains: why is it so slow? Its not bandwidth and its not CPU power...

[Schotty]

Allright, let me see what you mean with this...
Running apps on the remote box is what I want. I ssh -X my home computer to the remote host at school, and then run apps on the remote end, which display at home. Right?

Exactly.

But the question remains: why is it so slow? Its not bandwidth and its not CPU power...

You may very well have a bandwidth issue. Recall, that ethernet switches add latency to the TCP/IP connection to add security (main benefit is that nobody can sniff you). Add the fact that they may throttle connections at a router or server for certain things. UW Milwaukee did such things, and may very well do the same thing today. Local students get priority over remote students. Now, wat I would reccomend is this -- assuming you are not in a dorm -- goto a friends' dormroom and see if your exact setup works speedily or not. You may just have a slow NIC, crappy driver for your NIC, or even a shitty CAT5 cable (you are using CAT5 UTP, not CAT3, right?). Also, you may just ned a few tweaks on your TCP/IP stack. I found a good article on that from RedHat/IBM. Lemme dig that up and post it. try that first. It does require a kernel recompile however.

[Bartman]

Allright, but other apps (such as ftp), to the same server, also forwarded over ssh, usually get about 2Mbits/s. Which is a bandwidth I can very well live with. And latency? Average ping = 25ms

[Schotty]

Hmmm....

Well, what happens if a buddy at the dorm does the same thing? Can he get appropriate speeds? If not, I still would be apt to believe that the routing equipment is still a possible blame. But since its not your connection in general, you may have a crappy remote X server connection. Do a tcdump on your connection and see what it says. You may be retransmitting alot of data, hence sowing the connections' overall speed.