Headless desktop: what's the performance loss?

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Devil Master
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Headless desktop: what's the performance loss?

Unread postby Devil Master » Sat Apr 02, 2016 6:07 pm

I was browsing the wiki and I found the article about running SGI machines in headless desktop mode. The first thought I had was: "Wow, that's a really convenient way to avoid locating a compatible monitor!"
The second thought I had was: "Hold on, if data about what should be on the SGI machine's screen, as well as keystrokes and mouse movements, are being sent through a serial port... how much performance is lost?"

Really, isn't the serial port a huge (or should I say tight) bottleneck? If the SGI machine is constantly sending desktop data to the controlling machine, and the controlling machine interrupts the receiving stream for each keypress and mouse movement, what's the lag on such a setup? If I had to make a wild guess, I'd say the average performance is 5 frames per second, with a delay of .2 to .4 seconds between performing an action and seeing it performed on the screen. Is that close enough, or am I being too pessimistic? Or maybe... am I being too optimistic? :shock:

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Re: Headless desktop: what's the performance loss?

Unread postby vishnu » Sat Apr 02, 2016 9:44 pm

The X session doesn't go through the serial port it goes over IP (through the ethernet cable), the author's just mentioning the serial port for the sake of completeness, because it's the only way you can access the PROM without having a monitor attached... :mrgreen:
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Re: Headless desktop: what's the performance loss?

Unread postby Devil Master » Sun Apr 03, 2016 5:12 am

Oh, I see. So what would the lag be? Would it be feasible, for example, to use a headless desktop configuration to run graphical demos?

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Re: Headless desktop: what's the performance loss?

Unread postby jpstewart » Sun Apr 03, 2016 7:12 am

Devil Master wrote:So what would the lag be? Would it be feasible, for example, to use a headless desktop configuration to run graphical demos?

The only way to know is to try it and see.

It will depend on the graphics performance of whatever machine you're using to do the displaying. Both hardware and software can affect that. Likewise the network connection between the machines will play a big part. Local ethernet with little other traffic will perform very well. A congested network and/or multiple hops through multiple routers will not.

Also keep in mind that some demos may require some of SGI's proprietary extensions. So some demos may only work if the displaying machine is also an SGI.

That said, remote X11 works quite well in my experience for pretty much everything I've tried. That includes running Pro/E on a headless O300 with the display on a Linux box! Now, admittedly that was more to see if it would work than to do anything serious with it. I doubt it would be a pleasant experience with a complex model in Pro/E. But for doing simple stuff across a quiet LAN, it was surprisingly usable.

But really, you'll have to try it to see if your hardware, your software, your network can meet your performance expectations.
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Re: Headless desktop: what's the performance loss?

Unread postby shyouko » Sun Apr 03, 2016 9:33 am

If you are just running plain 2D X11 session in local wired LAN, it's pretty much native speed.

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Re: Headless desktop: what's the performance loss?

Unread postby robespierre » Sun Apr 03, 2016 10:24 pm

3D demos using GL or OpenGL won't run remotely without support on the remote server (either DGL, which is exclusively for IRIX; or GLX, which would need to be compiled in to the XServer). Performance for any kind of moving images over remote display is pretty slow. Remember that the machine running the client needs to take more of its (limited) cycles to create the packets and send them, even if the server side is fast.
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