Remote X session is slow [centos5]

Question

Okay, I've scoured google and I haven't found an answer for this. Not exactly programming related unless I was trying to use an ide over the session...

I have servers at the same remote location; one is older running fedora 4 (P4 3.0Ghz) and a couple of newer server running Centos5 (Quad Xeon 1.6).

I can run a remote X session on both at the same time and the Fedora server X window is nice and snappy but the Centos servers are slow and laggy. I connect to both vis ssh -X -C. I've tried without compression but it is still slow/laggy.

The two centos servers are not taxed at all by applications, one is a hot standby so it's not running anything really.

I've tried these kernels on the centos boxes:
2.6.18-92.1.22.el5xen
2.6.18-92.1.22.el5
2.6.18-8.1.8.el5

All these servers are on the same subnet and share the same routing path/switch etc.

Help!...

ps (I know I should only be using command line access but I am trying to make this easier for someone to "back me up" on occasion)

Answer 1

Most likely, you are flooding your network connection rather than the processor. The modern toolkits (QT/GTK) are much worse about network behavior than the older stuff. I've used VNC and NX to solve the problem in the past, and have had the best low-network use performance from NX. The FreeNX project is very useable if money is an issue. The only issue I've had with NX is I've never had reasonable sound, GLX, or XRender performance. But, that isn't really an issue for most people.

Answer 2

X11 forwarding can really saturate network, so the most probable cause is the difference in connections between these machines.

I'd recommend you use some protocol more optimized for network use, as NX or RDP.

Answer 3

I agree with you, Centos 5.x and RHEL 5.x have severe performance problem with applications launched over a slow link through ssh and X11 forwarding. I've filed a bug both with Centos and Redhat about this problem. Some applications (wireshark, system-config-lvm, ...) are totally unusable when launched remotely on v5 servers.