On Fri, 29 Jan 2010, Tom Kuiper wrote:
Dan Werthimer wrote:
each GPU can handle 100 to 200 MHz dual pol depending on whether
you are doing coherent dedispersion (timing), or spectroscopy (searching).
matthew and jonathan are the experts at reading data from ibob/roach and
using CPU cluster to do pulsar/transient search. john ford, paul demorest,
scott ransom et al are the experts at using ibob/bee2
to packetize data (800 MHz dual pol) for GPU based pulsar cluster
(see their fantastic GUPPI instrument).
We could have up to 1400 MHz at once, 8200-8600 and 31,500-32,500 MHz but I
think only one polarization. I saw that John Ford is using 8 GPUs for 800
MHz. Can you get several GPUs on the single bus of a multi-core host or does
that cause too much of a bottle-neck? I also should think about doing the
various piggy-back tasks in parallel. I'm guessing that setispec on a ROACH
is a tight fit. How about two? The kurtosis is a very light task, I think,
so can some of the left-over resources be used to expand the SETI bandwidth
or refine the resolution?
Anyway, for now it's some high-level wishing so I'll scope one unit at three
dual-channel ADCs, three ROACHes, two 4 core hosts, and 8 GPUs. Does that
seem reasonable? About $40K? (We have to pay Xilinx :-( .)
Thanks for your help
Hi Tom,
couple thoughts about the pulsar applications:
If your only frequency options will be 8 and 31 GHz there's probably not
too much point in doing coherent dedispersion.. unless you're interested
in sub-us time resolution (like Glenn's giant pulse stuff). We use it for
timing pulsars, but at much lower freqs, generally 0.3-2.0 GHz. You don't
need coherent dedisp for pulsar searches.
You mentioned real-time searching with GPUs. That could be an interesting
application, but I don't have a good feeling for how much BW/card is
possible in this case. In standard psr searches we record fast-sampled
spectra to disk (at 25-100 MB/s) then do the searching offline.
Also, most pulsars are pretty weak at 8 GHz, and extremely weak at 31 GHz.
The typical spectral index is something like -1.8.
Hope this helps!
-Paul
