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Top-Level Architecture
MWAX comprises 26 new servers and repurposes 10 of the existing servers on site at the MRO, occupying three racks. It makes use of the existing 100 Gbps fibre-optic link from site to the ten existing storage servers located in B206 on Curtin Campus. These ten servers will buffer MWA data pending transfer via a 100 Gbps fibre-optic link from B206 to the Pawsey Supercomputing Centre.
This configuration is capable of simultaneous fine channelization, cross-correlation, frequency/time averaging, and buffer storage for 256 tiles. In addition to the support for twice the inputs / four times the output visibilities, the MWAX correlator offers a number of improvements over the legacy system.
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Whereas the legacy correlator utilizes a polyphase filterbank for the F-engine, the MWAX correlator employs the FFT. For the X-engine, development time/cost has been minimized by utilizing the existing open-source GPU correlator library “xGPU” “xGPU” (the same library at the heart of the legacy correlator). The standard xGPU library is used essentially unchanged for MWAX, with the exception of a small but crucial change to improve speed and reduce bus/memory traffic, found to be essential to making the design scalable to 256T and beyond (see MWAX xGPU on github).
The 24 coarse channels are processed by 24 GPU-accelerated compute nodes referred to as “MWAX Servers”, with two ‘hot spares’. Each MWAX Server implements the functions shown in the figure below. The real-time data flows on the MWAX Servers are managed through the use of input and output ring buffers that decouple its computational workflow from the input source and output destinations. These ring buffers are established and accessed using the open-source ring buffer library “PSRDADA”.
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