[Beowulf] HPC demonstrations

Egan Ford egan at sense.net
Tue Feb 10 06:02:30 PST 2015

My favorite for lectures is PVMPOV.  I haven't run it in 15 years, but
the source is still out there.

PVMPOV will render a 3D image and let you observe the process
realtime.  The scene is split up in to N blocks of size M and
distributed to P processes.  Each process works on a single block at a
time.  Hard to render blocks take longer than easy blocks.  And this
is obvious as you watch it.

Experiments you can do with this demo:

1.  Make the block size very small 1x1 or 2x2, etc... this will smooth
out the runtime for each block, but the overhead of orchestration and
communications will slow you down.
2.  Make the blocks really big, 64x64, 128x128, etc... this will
reduce comm, but a single block could slow down the entire job.  Too
bad the code doesn't break down hard blocks by dynamically changing N
and M.  IIRC the Mandelbrot demo does--also another good visual demo
you can run on a single laptop.
3.  Try a different number of processes

I like this demo because I can lecture on parallelism, efficiency of
scale, inefficiencies of unbalanced or overly chatty decomposition.
Limits to scale, etc...

You can run this on your laptop with a single Linux VM.  You can
adjust the time of the demo based on the complexity of the scene and
the target size, there are many freely available POV models.

Lastly, PVM has fault recovery.  If you like, kill a process while mid
block.  At the end, missing blocks will be re-rendered before end of
job.  This can lead to discussions about failures at scale and the
importance of checkpointing and/or code that can recover.  The last
very large system I built had a conservative MTBF of 23 hours because
of the volume of memory DIMMs (after a year of observation it was more
like 48-72 hours).

On Tue, Feb 10, 2015 at 3:52 AM, John Hearns <John.Hearns at viglen.co.uk> wrote:
> I am giving an internal talk tomorrow, a lightweight introduction to HPC.
> Can anyone suggest any demonstrations of HPC which I could give – something
> visual?
> Or are there any videos I could pick up from somewhere?
> I ahad thought on showing an H-bomb test video from Youtube, and saying
> “Well, you aran’t allowed to do that any more”
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