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By | Timothy Prickett Morgan 17th November 2008 14:02

Supercomputing past masters resurface with coder-friendly cluster

Convex Convey boasts unified programming

SC08 The Supercomputing 2008 show in Austin is going to be the occasion for a lot of flashbacks, and not just because there are countless nerds on hand who came out of the University of California at Berkeley. The event is hosting the debut of a new supercomputer maker, Convey Computer, and the company's brain trust includes Steven Wallach, the man who co-founded vector minisupercomputer maker Convex Computer in 1982.

The Convey Hybrid Core-1 supercomputer is a cluster of two-socket, run-of-the-mill servers using Xeon processors from Intel. And like many experimental supercomputers being developed these days, the HC-1 also uses field programmable gate arrays (FPGAs) to substantially accelerate the performance of the applications running on the x64 processors. The machine does, of course, run Linux.

Other supercomputer makers and research projects in government, academia, and industry have been playing around with FPGAs as well as using graphics processing units to boost application performance, but there is some secret sauce that Wallach and his team at Convey have come up with to make this a little bit easier on the programmers.

First, the FPGAs used in the HC-1 don't plug into the server I/O or the graphics ports. They drop into one of the two processor sockets on the board. And because Convey has licensed both the frontside bus used with current Xeons and QuickPath Interconnect that will be used in future Xeons, Convey has done something really clever. It has linked the FPGA to the x64 processor in a cache-coherent manner.

While the details of what Convey has done are complex, the practical effect is one many of us can remember: It is akin to plugging an 8087 floating point math unit into a motherboard on an old 8088-based PC. You don't have to do any special programming. When the main CPU needs to do math, it hands it off to the much-faster co-processor.

"This is our fundamental breakthrough - a single programming model," says Bruce Toal, one of the company's co-founders and its president and chief executive officer.

Toal, by the way, was one of the bigwigs at the former Convex, which was eaten by Hewlett-Packard in 1995 and whose technology was part of the underpinnings of the high-end HP 9000 V-class and Superdome PA-RISC servers. And for many years after the HP acquisition of Convex, he ran HP's supercomputing business.

In 2007, Toal was approached by Wallach and his former co-founder at Convex, Bob Paluck, now a venture capitalist, to evaluate the possibility of bringing a hybrid x64-FPGA supercomputer to market. By the summer, Toal had signed up Intel and Xilinx, a maker of FPGAs, as well as Centerpoint Ventures, InterWest Partners, and Rho Ventures, as venture backers, raising a total of $15.1m in funding.

Programmers wanting to use FPGAs to accelerate their code in the HC-1 get an FPGA that has been programmed with a "personality" that is tuned to a particular type of application. One personality makes it behave like a vector math unit (called the SPvector personality), which is useful for seismic processing in the oil and gas industry. Another, called the financial vector personality, which is still in development, replaces pairs of single-precision math units in the SPvector personality with double-precision units. It is being tuned to do lots of parallel random number generations, which financial modeling software requires. Yet another FPGA is programmed to have a personality suitable for accelerating the calculations used in protein sequencing applications.

Memory architecture secret sauce

Another secret sauce in the HC-1 is the memory architecture. The FPGA and its personality are plunked on a chip that has 16 memory channels reaching out to the system, providing 80 GB/sec of bandwidth into the FPGA. The x64 processor and the FPGA are linked together with a cache-coherent shared virtual memory space, and applications see the x64 instruction set and a set of co-processor instructions implemented in the FPGA's personality.

Programmers using standard C, C++, and Fortran compilers will be able to see these extra instructions implemented in the FPGA and can make use of them in their code. Convey has spent a lot of time making the debugging for the x64 and FPGA co-processor environment seamless, says Toal, and the resulting applications created using the HC-1 applications can run on regular x64 servers or on the HC-1. Applications do require a Convey-enhanced (and Linux Standard Base-compliant) Linux kernel to make use of the FPGA co-processors and their personalities.

The HC-1 system boards have four DIMM channels for the single x64 processor and 16 DIMM channels for the FPGA, which are linked to each other through the front side bus architecture (as x64 processors are in two-socket machines) and, in the future, through the QPI point-to-point interconnect. The Convey machine uses standard DIMMs that have been optimized for cache line transfers (sequential access) and also has a special set of scatter-gather DIMMs that have been optimize for 8-byte transfers (random access). The Xeon side of the system can support up to 32 GB of main memory for applications using 8 GB DIMMs, while the co-processor side of the system board can support up to 128 GB of memory.

The development tools created by Convey for the HC-1 are derived from the Open64 compiler set that is available for Itanium processors, which are themselves open source versions of the tools created by Silicon Graphics for its MIPS supercomputers. The Open64 tools have been ported to the x64 architecture and extended with lots of goodies by contributors in industry and academia. The HC-1 development tools also include features so customers can create their own custom personalities for the FPGAs, tuned specifically to accelerate calculations in their own applications.

With supercomputers, people want to know about performance. And here's the real reason why Wallach, Toal, Convey's investors, and the company's 33 employees are all excited about the HC-1. "Commodity platforms have flattened, and more and more cores have not resulted in more performance. We looked at the problem with a certain amount of déjà vu, back to the days when machines had attached vector processors." And the resulting HC-1 machine gives a performance boost on math routines just like those vectors of days gone by.

In early benchmark tests, the HC-1 running a protein sequencing application (an actual application running at Convey's first customer, the University of California at San Diego) showed a factor of 16 improvement in performance compared to a single two-socket Xeon box running the same code. Performance will vary depending on the application and the implementation of the FPGA personality, of course.

The HC-1 will begin shipping to beta customers in February 2009 and will be in full production in the second quarter of next year. A base HC-1 machine with a quad-core Xeon processor and 4 GB of memory on one side and the FPGA co-processor and 8 GB of memory on the other side costs $32,000. If you do the math, that's roughly 16 times the math oomph for about half the price of 16 reasonably configured two-socket Xeon boxes.

This might not be a tough sell at all, if the programming is as elegant as Toal says it is. ®

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