On 9/15/2010 9:03 AM, Nivedita Singhvi wrote:
Klaas van Gend wrote:
On Wednesday 15 September 2010 05:38:49 jordan wrote:
Which leads me to my last example. Most people are aware that since
about 1999-2000, Linux has dominated the movie industry. Beginning
with Titanic and even today with say, Avatar.
I would be willing to bet, that all of those wonderful rendering farms
and production suites, are
in fact using rt-linux.
Please put a lot of money on that bet, because I'd like to win it :-)
Why would those rendering farms use rt-linux?
Rendering is not done in real-time - far from it actually. It can
take minutes of the entire farm to render a single frame. So
rendering is nothing but CPU-
intensive (calculating how all those lightbeams are reflected by each
surface) - and everything I/O bound is about throughput: writing the
rendered pixels to disk and getting more surfaces from disk.
There are no deadlines for rendering, there are no penalties if a
frame is late by seconds - if the farm cannot complete its job
overnight, they'll add more CPU power.
While all of the above is true, I'll add that it's worth testing
RT because certain applications which have lock-step operations,
can be very negatively impacted in throughput by severe lack of
determinism. If all of a set of operations need to complete before
they can do the next set of operations, and one of the threads takes
very long, the others all idle as a result. If this happens frequently,
you're better off trying to cap max latencies.
So RT actually provides improved *throughput* as well, despite the
increased overhead.
I don't know if these rendering type applications necessarily
fall into that bucket, but I would at least take a look.
thanks,
Nivedita
I haven't messed with rendering much since the Amiga days, but my
understanding is that a given CPU could render anywhere from just a
single pixel to entire frames independent of the work on any other
processor. Raw CPU, cache hits and fast memory win. High bus/network
bandwidth and storage sweep up the pieces. I would try to use the
lightest kernel I could get by with, boot from network and run from RAM
with only the services necessary to get scene info in and rendered
pixels out. In my mind, a render box should be single purposed with few
competing processes. I suspect that determinism is much less important
than efficiency here.
Then again, it may still be cheaper to "add more CPU" than to give more
than cursory attention to the kernel or OS. It may be the case where
Linux or *BSD have been used in render farms because of license cost,
not for any particular technical merit!
/ducks
-Reagan
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