Hi Tom, One of the main bandwidth limitations in pulsar processing is the length of the dedispersion "chirp" function, which goes down quadratically with increasing frequency. Generally people split the band up into several ~4 MHz channels and coherently dedisperse each one separately. Each of these channels will have a very short chirp response, something like 50 microseconds at 8 GHz even for a high DM of 1000, so I'm pretty sure you're going to be limited by I/O bandwidth rather than processing power. You can run up to one GPU per processing core, but I don't have experience myself with where the bottleneck would be.
Also keep in mind that timing pulsars may not be a good piggyback operation since you need to dwell on the pulsar for a few minutes. Glenn On Fri, Jan 29, 2010 at 4:17 PM, Tom Kuiper <[email protected]> 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 > > Tom > >
