[Spice-devel] Performance of Xspice - some results, and a potential patch

[John A. Sullivan III]

On Mon, 2012-08-06 at 15:12 -0500, Jeremy White wrote:
<snip>
> For a test involving 5 minutes of light use of LibreOffice, the results
> are as follows:
> 
> 		 Packets	  Bytes
> Xspice		148,428		19,647,168
> Tight VNC	 19,980		 4,724,880
> SSH -X		 48,894 	77,733,200
> SSH -CX		 21,445		 5,096,702
> 
> You can see that Xspice network performance is pretty bad.
> 
> This is partly by design; Spice is designed to replicate the philosophy
> of the X server, wherein graphics operations themselves - not pixmaps -
> are transmitted across the wire.
> 
> Further, Spice as a whole is really built around qemu and Windows qxl
> running on a local LAN; Xspice is really just an experimental feature,
> and I'm pretty much the first person to examine it's network flow.
> 
> However, if I modify the xf86-video-qxl driver to shift modes into a
> render and send mode, whereby only changed pixmaps are sent across the
> wire (and that on a periodic basis), I get dramatically better results.
>  That patch is attached; these are the results:
> 
> Xspice + deferred_fps  14,910 	2,971,886
> 
<snip>
I'm very encouraged to hear this as we are very, very interested in
SPICE as a WAN protocol.  We have noticed that the end user experience
is almost as dependent upon latency as bandwidth so I was a little
concerned that you are sending pixmaps changes on a periodic basis.
Does that introduce any noticeable latency?

I've been quite surprised at how much users are affected by latency I
would not have thought an issue.  Thus, I would define noticeable as
somewhere between 50 and 100 ms.  Thanks very much - John