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

[John A. Sullivan III]

On Tue, 2012-08-07 at 08:08 -0500, Jeremy White wrote:
> > I don't know what were the network conditions you tested, but it would be great if you could repeat your test with lower bandwidth (you can use tc), and also, you can try disabling off-screen surfaces in the driver.
> 
> I do have a test network constructed for just that purpose, so I
> can manage and measure all aspects of the network.
> 
> It was with the latency set to 80 ms that I probed the issue with the
> ack window size.
> 
> For the tests I ran, though, I was on an uncrippled network, using
> all default settings for Xspice.  I do not know what form of image
> compression was in use; only that it would be whatever default would
> be chosen (I believe the default is auto lz, and my sense is that
> I was mostly seeing lz and quic images going across the wire, but
> don't quote me on that).
> 
> As far as I recall, disabling surfaces prevented Xspice from
> working properly, so I did not test that mode.  I did not really
> understand how to analyze the effectiveness of surface caching,
> so while I saw the ability to gather those statistics, I didn't
> do that exercise.
> 
> I haven't tried throttling bandwidth; it's interesting to know that the code
> may respond to that condition.
> 
<snip>
In our traces, we saw exactly that.  There is at least an initial
negotiation (I do not know if there are subsequent ones) and I think the
threshold is pretty high by WAN standards.  I forget if it was 5Mbps or
10Mbps when it auto-changed its algorithms.

In our testing on fairly standard (if there is such a thing) American
cable and British DSL connections, the user experience other than video
was quite acceptable other than for the latency.  There was some talk of
changing the streaming video algorithm from mjpeg to an inter-frame
compression method but I don't know where that stands.

So, from our limited user testing, latency and inter-frame video are the
big remaining issues.  Thanks - John