Hi Jack, Thanks for the great points you raise.
I did consider previously a ‘hack’ to get short integer arithmetic out of 32-bit words, but the Tensor cores look very attractive now when they do this directly. Certainly, I have to re-evaluate the GPUs, given the costs and the potential less difficult programming of, it needs serious consideration. Many thanks, Neil From: Jack Hickish <[email protected]> Sent: 15 August 2020 18:49 To: casper <[email protected]> Cc: Danny Price <[email protected]> Subject: Re: [casper] references to recent cross-correlator technology developments I'll join the group of people who aren't Danny responding to your message :) These days GPUs have much better non-floating point performance -- Nvidia's tensor cores will do INT8 / INT4 compute which are (I gather) good for machine learning. The Tesla T4 card specs specifically state low-precision performance numbers. Even before this trend, operations like 8-bit, 4-element dot-product were around, and are used to great effect in the xGPU library. And even before that, the cunning and guile of users could do things like coerce 32-bit integer arithmetic to perform multiple 4 bit operations per cycle (see, for example, the CHIME correlator). So while it is true that FPGAs still have an edge in performing arbitrary precision operations with high efficiency, GPUs are fighting in that space too. Cheers Jack On Sat, 15 Aug 2020 at 05:37, Neil Salmon <[email protected]<mailto:[email protected]>> wrote: Hi Danny, GPU’s may be starting to rival FPGA’s in processing power for correlators. However, are GPU’s restricted to long word correlation, say 32-bit floating point, whereas in FPGA I’m assuming the bit length is variable, so you may choose say 4-bit integer correlation – which would match to a 4-bit ADC. If you can’t adapt the word length for GPU correlators, then the FPGA technology still has an edge, because as far as correlation is concerned, I’m not sure if going to word lengths longer than 4-bit is resourceful use of silicon real estate? What is your view on that? I did include a section on correlators in the document on security screening imaging https://ieeexplore.ieee.org/document/9154708 and some of your selected publications in the references – thank you. Cheers, Neil From: Danny Price <[email protected]<mailto:[email protected]>> Sent: 20 July 2020 14:44 To: Neil Salmon <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]> Subject: RE: [casper] references to recent cross-correlator technology developments Hi Neil, The correlation is indeed done in real time using stream processing frameworks for most interferometer telescopes. Conversion from (very sparse) visibilities to images is generally done offline (this can be very time consuming!). There are a few real-time imaging systems: the EPIC correlator that Jack mentioned, and the realfast system on the VLA (https://science.nrao.edu/facilities/vla/observing/realfast) are good examples. Cheers, Danny On 20 July 2020 at 9:55:06 pm, Neil Salmon ([email protected]<mailto:[email protected]>) wrote: Hi Danny, Thank you for these references. For security screening systems the name of the game is real-time, ie an image in less than 1 second. However, I see a great many references to GPU based correlators. I was used to seeing these devices as off-line correlators, as in software correlators. Are the GPUs being used by the radio astronomy community as real-time correlators, or as software correlators? Many thanks, Neil From: Danny Price <[email protected]<mailto:[email protected]>> Sent: 20 July 2020 12:21 To: [email protected]<mailto:[email protected]> Subject: Re: [casper] references to recent cross-correlator technology developments Hi Neil, To add to Jack's post, allow me to plug some overview articles that may be of interest. The first, https://arxiv.org/abs/1702.00442, was for an introduction for a special issue of JAI on DSP in radio astronomy in 2016. Table 1 summarises some of the larger correlators: the references therein may be of use. Jack (et al)'s CASPER article in said JAI special issue is also a font of references: https://arxiv.org/abs/1611.01826. The full special issue article listing is up here: https://www.worldscientific.com/toc/jai/05/04. More recently, here's my book chapter on real-time stream processing in radio astronomy, https://arxiv.org/abs/1912.09041, which delves a bit deeper into technical details for common approaches. In terms of cutting edge, there are various groups working with the Xilinx RFSoC components for next-gen systems -- you will no doubt have seen some traffic on this list. The ASKAP telescope group have plans to use an Alveo Xilinx U280 accelerator card for high time resolution imaging + dedispersion, which is an alternative to the GPU correlator. GPU correlators are still the most widespread for O(100) antennas. There's some discussion on GPU correlator performance in J. Kocz et al 2014 (https://arxiv.org/abs/1401.8288); for O(100) inputs a GPU correlator will likely be memory bandwidth bound. Cheers, Danny On 18 July 2020 at 7:54:49 pm, Neil Salmon ([email protected]<mailto:[email protected]>) wrote: I need references on recent developments in cross-correlator technology for an IEEE paper on the subject of aperture synthesis imaging in the area of security screening of people for concealed weapons. Typical requirements for this application are cross-correlators that can process in real-time signals from hundreds of receiver channels with around 1 GHz of RF bandwidth. As none of this technology is commercially available off-the-shelf I’m dependent on the radio astronomy community to get the latest information of correlator development. This might be just technical knowhow on the building of correlators, or communities who would be willing to supply for a fee correlators to a security screening technology development company. Could anyone provide me with any references of papers on recent correlator development that I could include in this paper? Many thanks, Neil "Before acting on this email or opening any attachments you should read the Manchester Metropolitan University email disclaimer available on its website http://www.mmu.ac.uk/emaildisclaimer " -- You received this message because you are subscribed to the Google Groups "[email protected]<mailto:[email protected]>" group. 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