[Verse-dev] Verse performance

[Emil Brink]

Eskil,

I've done some simple benchmarks of downloading a large bitmap, inspired
by the ... non-perfect results I've seen so far from Toni's testing.

What I did was draw a magnificent 5120x5120-pixel 8-bit RGB test image,
since that size is what the Orangers like to use. I drew this in the
GIMP, using every ounce of my artistic talent. And a few filters good
at filling out the image. Anyway, I saved it as a nice 44 MB PNG, and
uploaded it using pngload from the verse-tests/ module.

Uploading performance isn't exactly stellar; it takes 2:18, i.e. two
minutes and 18 seconds. But it's download that I want to talk about.

What I did next, was instrument the Verse Bitmap Viewer (vbv) with
some simple code to keep track of:

For the first tile:
* The time when the first tile arrives

For all other tiles:
* The number of tiles that have arrived
* The total time taken since the first one

I use this to compute the tiles/second speed of the download, which is
then printed for each tile. Sample output goes like this:

[... more ...]
count=13099, dt=5.28211 -> 2479.9 tiles/second, 1228800 tiles total
count=13100, dt=5.28218 -> 2480.0 tiles/second, 1228800 tiles total
count=13101, dt=5.28225 -> 2480.2 tiles/second, 1228800 tiles total
count=13102, dt=5.28232 -> 2480.4 tiles/second, 1228800 tiles total
count=13103, dt=5.28239 -> 2480.5 tiles/second, 1228800 tiles total
count=13104, dt=5.28246 -> 2480.7 tiles/second, 1228800 tiles total
count=13105, dt=5.28254 -> 2480.8 tiles/second, 1228800 tiles total
count=13106, dt=5.28261 -> 2481.0 tiles/second, 1228800 tiles total
[... much more ...]

What's more; this is very "bursty", it looks as if N tiles arrive
close to each other in time, then there's a short pause, then another
burst, and so on. I guess this is because the server does other
things as well, but it's very obvious and somewhat annoying. The
value of N is a bit hard to measure with my current code, but might
be ~2000 or so.

Anyway, the above tiles/second number can be used to compute a rough
ETA for the download as a whole:

         1,228,800 tiles
        ----------------- =~ 500 seconds
         ~2,500 tiles/s

Thus, this download is going to take almost ten minutes. Is this the
expected performance? It's not usable for the purpose of painting
textures for film-making, with these kinds of delays.

The numbers seen by Toni at Orange, taken with Gimp as the downloading
application, are *far* worse, about three **hours** to download an
image this size. This *might* be because of local factors like doing
a refresh of the image is taking time, though.

Any comments?

Regards,

/Emil