[IPython-dev] matplotlib webagg benchmarks

MinRK benjaminrk at gmail.com
Wed Aug 7 19:08:28 EDT 2013

On Tue, Jul 30, 2013 at 2:28 PM, Michael Droettboom <mdroe at stsci.edu> wrote:

> As promised in last week's Google Hangout to the IPython developers
> meeting -- I have some concrete timings and numbers on the matplotlib
> WebAgg backend in a couple of different scenarios.
> First, let me apologize -- the way I was timing binary websockets vs.
> text websockets previously was wrong.  The actual impact of it is much
> smaller than I had originally estimated -- so the discussion about
> whether to include binary websockets in IPython may have been all for
> naught.

Part of our message spec includes binary blobs trailing after the JSONable
message dicts.
Currently this is used by `data_pub` and `apply` messages, but it could
theoretically be extended to display data for streaming output, such as
video or audio.  Right now, we have no way of propagating that part of the
message spec up to notebook frontends, because we do not yet have any
binary messages that the notebook frontend can understand.  In these cases,
a switch to binary websocket may still make sense, even without a
performance argument.

> For benchmarking, I used two different plots.  One is the classic
> "simple_plot.py" sine wave, which tests sort of the "easy case" where
> very little of the image is updated in each frame, and the other was
> "animation/dynamic_image.py" in which most of the plot is updated in
> each frame.
> I tested both scenarios with client and server on my local machine, and
> through an ssh tunnel that goes over wifi, the public university
> network, to my home's 15/5 MBps cable connection 28 miles away and back.
> For (A), the average frame weighs in at around 20kb.  For (B), it's
> around 90kb.  For base64, multiply by those numbers by 4 / 3.
> On my local machine, I can push through about 18 fps, so a bandwidth of
> 2.8MBps (were it sustained, which it rarely is).  On the tunnel, I
> fluctuate between 7 and 10 fps, which is quite usable, and quite near
> the practical upper limit on the bandwidth of that connection.
> However, the problematic thing for the remote connection is the
> latency.  Locally, I average a fairly steady 250ms to roundtrip from a
> mouse event to an updated frame.  Remotely, it fluctuates randomly
> between 400ms (still usable) and 3000ms.  Some more careful dynamic
> scaling of events can probably make that easier to use, perhaps.  I know
> games often use UDP and handle robustness to packet loss in a different
> way as a way to remove some of the latency of TCP.  I have no idea if
> such a thing would be possible over a web socket, of course.
> I could not measure any statistically significant change in framerate or
> latency between a binary websocket and a non-binary one.  However, there
> is a 10% increase in CPU time on both the python side and the browser.
> It so happens that I wasn't saturating my CPU, so it had no net impact.
> Likewise, I am not saturating my bandwidth, so the additional size
> doesn't matter in this case.  But I suspect if either one of those
> resources is starved, the additional 10% cpu time and 25% bandwidth
> increase may matter.

Thanks for these numbers - I suspect the potential penalty for an extra hop
between the kernel and the notebook will not be significant in any case
where the kernel is local to the server and the client is remote.


> Mike
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