[FreeNX-kNX] Forcing the graphical applications to use the server-side graphics abilities

[Prakash Velayutham]

Hi Mario,

I am back to this issue I was working on a while ago.

On Mar 20, 2009, at 12:58 AM, Mario Becroft wrote:

> Prakash Velayutham <prakash.velayutham at cchmc.org> writes:
>
>> These are my experimental numbers.
>>
>> Client X (using NoMachine client)
>> FreeNX server Y
>> Graphics node Z
>>
>> I connect via the NX client from X to Y (using SSH tunneling and X
>> proxy)
>> I then SSH -X to the graphics node (this is needed in my setting as
>> the graphics node Z is in a private network reachable only from Y)
>> Then I startup Matlab on the node. This, if I am correct, streams all
>> the OpenGL rendering commands through the tunnel back to my client  
>> and
>> uses the client-side X (which is the X server here) to render it.  
>> And,
>> by the very definition, this cannot use hardware acceleration as it
>> can only do indirect rendering. My Matlab startup time, as I see it,
>> is about 27 seconds in this case.
>
> If you were directly running X protocol without using NX, or using
> nxproxy without nxagent, this would be at least partly true. The GL
> commands would be sent via GLX protocol to the X server, which, as I
> understand it, should still be able to use the accelerated graphics
> hardware to do rendering if it wants to. However, in practice the
> performance can be very poor. I am hazy on the details of direct
> vs. indirect rendering in GLX, so I may not be quite right about this.
>
> However, if you are using nxagent, which is the usual way NX is used
> since it provides round-trip suppression, then this will not be the
> case, since nxagent does not support forwarding GLX requests (as far  
> as
> I know).

Yes. I do use nxagent.

>
>> What I have read thus far says that a VNC connection renders the
>> graphics on the application side, instead of the interaction side.  
>> So,
>> if, after connecting to node Z, I start up a VNC server on, say
>> display 1, and then connect to Z from Y using a VNC viewer, and start
>> up Matlab, the startup time, is about 10 seconds.
>
> Yes, if you use ordinary VNC, then the Mesa software renderer built  
> into
> Xvnc will do the GL rendering, and bitmap data (compressed using  
> normal
> VNC protocols) will be sent to the VNC client.
>
> Where something like VirtualGL comes in is that it enables the  
> graphics
> rendering to be done on OpenGL hardware other than the video hardware
> the VNC client is displaying on. Typically this is used to do  
> rendering
> on a host close to the one running the GLX client (possibly the same
> host), while sending the resulting images through VNC or NX protocol  
> to
> a remote host. The remote host need not have accelerated graphics
> hardware.
>
> Assuming you were using nxagent in your NX test, it is not clear to me
> why there is a performance difference between NX and VNC in this
> case. Maybe you were not using an nxagent session, and your GLX  
> commands
> were being sent all the way to the NX client.
>
>> I am trying to understand which is the best way to extract the
>> rendering power of the graphics node and still get the best
>> interactive experience using NX.
>
> Assuming you are using nxagent, which does not forward GLX to the  
> remote
> X server, your options are twofold:
>
> 1. use NX in the normal way. Rendering for GLX clients will be done by
> the Mesa library in the nxagent running on the nxagent host's CPU.
>
> 2. use NX in combination with VirtualGL or similar, and configure
> VirtualGL to use a video adapter locally attached to the host running
> nxagent (or possibly another host on a fast LAN).

What do you mean by a video adapter here? A 3D graphics card? Do you  
have this setup? Definitely, option 2 is what I am trying to achieve,  
I just don't know what I am missing though.

> In both cases, the rendering is done on the server side of the NX
> connection and the resulting images are sent to the client using  
> normal
> NX image compression. 1. will be slow since the rendering is done on  
> the
> host's general-purpose CPU. 2. will be much faster since rendering is
> done on accelerated graphics hardware.
>
> There is actually a third way: if you link your GLX-using client  
> against
> Mesa, then the client can do all the rendering itself and just send
> images to the X server. If the X client and the nxagent are running on
> the same host, the end-result of this will be much the same as 1.
>
> Whether you need to use hardware acceleration or software rendering  
> will
> be sufficient depends on the type and amount of rendering work being
> done.
>
> -- 
> Mario Becroft <mb at gem.win.co.nz>

Thanks,
Prakash