On Tue, 10 May 2011 14:09:41 -0500
DRC <dcomman...@users.sourceforge.net> wrote:
> An accurate measurement of BWmax is critical
> here, though, and I don't really trust that there is a way to measure
> that accurately.
After trying TigerVNC's BWmax measurement, and trying to do more or less the
same in TurboVNC, I am not too confident with the timing method to know BWmax.
I'm just throwing out an idea: perhaps we can determine BWmax empirically.
1-Determining BWmax automatically
My idea is to start TurboVNC with a high quality. When the network is the
bottleneck, it will be loaded at 100% in this setup, so every two seconds apply
if (bw > max_bw)
max_bw = bw;
(using some smoothing is a possibility but I try the simplest first)
This gives a rough estimate of the maximal bandwidth - note that max_bw is
always increasing, so every 30 seconds we re-evaluate it.
To do that, my idea is to reset it, and force an increase in quality to
load the network, and re-estimate the bandwidth :
max_bw /= 2.0;
appData.qualityLevel += 10;
It's a hack, but I'm convinced that evidence-based empirical BWmax computation
is the only way to make this work - otherwise it's way too imprecise.
My testing shows pretty good results.
2-Special case: specifying BWmax
As per my first mail in this thread, I have added -autoqual-bw as a commandline
option, used to set up a known, constant BWmax. Useful when the user knows the
bandwidth of the network, or to limit how much BW is consumed by the viewer.
If you have a single viz node with a gigabit link and a standard provision of
10 users, you can use -autoqual-bw 12000 to limit each viewer to 12MB/s.
3-If you want to force reevaluating BWmax
Request an ALR or manually set a high quality for JPEG, this will overload the
network and speed up BWmax's increase
4-What do do with BWmax
Using this to apply the algorithm we talked about earlier (target BW = 90%-95%
BWmax) seems, on my limited testing done in my specific environment, to work
relatively well in picking the quality.
See at the bottom of this message for an output example.
5-When does this apply
This is useful when :
- the network is the bottleneck (this is the case on my 100Mbit/s connection
with 2*2GHz CPUs on each side, by the way).
- if you expect BWmax to vary during runtime because of e.g. congestion
(otherwise use -autoqual-bw)
- on a low latency network (I haven't tested this on a high latency network yet,
but it will lead to underestimate BWmax and set a quality that is
too low, perhaps this isn't a big problem)
- at any rate, it can be disabled
6-Status
This is merely a prototype that worked in a very, very limited test setup, but
I've been building understanding and experience with VNC those past weeks, and
I am more confident in this try than in the previous ones.
Automatic quality adjustment is a very hairy issue, and I think a not-so-great
implementation is better than the current none-at-all state of TurboVNC, and
the static-and-inaccurate technique used by TigerVNC.
What are your feeling about this? When I have done more testing I'll be able to
show an actual patch (there is very little code, in fact).
7-Some output examples
(Note that it changes the quality way too often, but that's easy to fix and for
later!)
100Mbit/s
Bandwidth 9511.44 kB/s (2.01 seconds)
Last BW sample is outdated, resetting max_bw to 0.000000
quality set to 95, subsampling 2
Bandwidth 11013.35 kB/s (2.02 seconds)
max bw 11013.351562 Link used at 100%
quality set to 85, subsampling 1
Bandwidth 6865.89 kB/s (2.01 seconds)
max bw 11013.351562 Link used at 62%
quality set to 87, subsampling 1
Bandwidth 7224.38 kB/s (2.00 seconds)
max bw 11013.351562 Link used at 65%
quality set to 89, subsampling 1
Bandwidth 7840.85 kB/s (2.00 seconds)
max bw 11013.351562 Link used at 71%
quality set to 91, subsampling 1
Bandwidth 8603.68 kB/s (2.01 seconds)
max bw 11013.351562 Link used at 78%
quality set to 93, subsampling 1
Bandwidth 9719.05 kB/s (2.00 seconds)
max bw 11013.351562 Link used at 88%
quality set to 95, subsampling 1
Bandwidth 11172.56 kB/s (2.02 seconds)
max bw 11172.559570 Link used at 100%
quality set to 85, subsampling 1
Bandwidth 6854.07 kB/s (2.01 seconds)
max bw 11172.559570 Link used at 61%
quality set to 87, subsampling 1
Bandwidth 7208.06 kB/s (2.01 seconds)
max bw 11172.559570 Link used at 64%
quality set to 89, subsampling 1
Bandwidth 7841.28 kB/s (2.00 seconds)
max bw 11172.559570 Link used at 70%
quality set to 91, subsampling 1
Bandwidth 8647.85 kB/s (2.00 seconds)
max bw 11172.559570 Link used at 77%
quality set to 93, subsampling 1
Bandwidth 9721.50 kB/s (2.00 seconds)
max bw 11172.559570 Link used at 87%
quality set to 95, subsampling 1
4500kB/s (simulated by trickle -d 4500, so kind of inaccurate)
Bandwidth 3530.50 kB/s (2.02 seconds)
Last BW sample is outdated, resetting max_bw to 0.000000
quality set to 95, subsampling 2
Bandwidth 3185.69 kB/s (2.05 seconds)
max bw 3185.692383 Link used at 100%
quality set to 85, subsampling 1
Bandwidth 3768.04 kB/s (2.01 seconds)
max bw 3768.036133 Link used at 100%
quality set to 75, subsampling 1
Bandwidth 3595.85 kB/s (2.03 seconds)
max bw 3768.036133 Link used at 95%
quality set to 65, subsampling 1
Bandwidth 3569.32 kB/s (2.01 seconds)
max bw 3768.036133 Link used at 94%
Bandwidth 3626.69 kB/s (2.03 seconds)
max bw 3768.036133 Link used at 96%
quality set to 55, subsampling 1
Bandwidth 3669.86 kB/s (2.00 seconds)
max bw 3768.036133 Link used at 97%
quality set to 45, subsampling 1
Bandwidth 3599.94 kB/s (2.00 seconds)
max bw 3768.036133 Link used at 95%
quality set to 35, subsampling 1
Bandwidth 2776.69 kB/s (2.03 seconds)
max bw 3768.036133 Link used at 73%
quality set to 37, subsampling 1
Bandwidth 2873.82 kB/s (2.01 seconds)
max bw 3768.036133 Link used at 76%
quality set to 39, subsampling 1
Bandwidth 2978.42 kB/s (2.01 seconds)
max bw 3768.036133 Link used at 79%
quality set to 41, subsampling 1
Bandwidth 3018.48 kB/s (2.03 seconds)
max bw 3768.036133 Link used at 80%
quality set to 43, subsampling 1
Bandwidth 3145.13 kB/s (2.01 seconds)
max bw 3768.036133 Link used at 83%
quality set to 45, subsampling 1
Bandwidth 3214.31 kB/s (2.00 seconds)
max bw 3768.036133 Link used at 85%
quality set to 47, subsampling 1
Bandwidth 3310.21 kB/s (2.02 seconds)
max bw 3768.036133 Link used at 87%
quality set to 49, subsampling 1
Bandwidth 3370.77 kB/s (2.02 seconds)
Last BW sample is outdated, resetting max_bw to 1884.018066
quality set to 59, subsampling 1
Bandwidth 3729.38 kB/s (2.01 seconds)
max bw 3729.376709 Link used at 100%
quality set to 49, subsampling 1
Bandwidth 3415.06 kB/s (2.02 seconds)
max bw 3729.376709 Link used at 91%
Bandwidth 3386.41 kB/s (2.04 seconds)
max bw 3729.376709 Link used at 90%
--
Greetings,
A. Huillet
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