It was a week for chip launches with the Hot Chips conference setting the stage for the unveiling of the IBM Power9 processor (report forthcoming) and a custom ARM-based 64-core CPU from Chinese firm Phytium Technology. A 25-core, open-source academic processor out of Princeton University also made its debut from the Silicon Valley event.
Piton – the name refers to the metal spikes used by rock climbers – was designed to be fast, highly scalable and energy-efficient in order to satisfy the demands of modern-day massive-scale datacenters. The Princeton University researchers say it’s possible to string together 8,000 of these CPUs to build a 200,000 core machine.
“With Piton, we really sat down and rethought computer architecture in order to build a chip specifically for data centers and the cloud,” said David Wentzlaff, a Princeton assistant professor of electrical engineering and associated faculty in the Department of Computer Science in an official announcement. “The chip we’ve made is among the largest chips ever built in academia and it shows how servers could run far more efficiently and cheaply.”
Piton is based on the SPARC V9 64-bit ISA and supports Debian Linux. After being designed in early 2015, Piton was taped-out in IBM’s 32nm SOI process. The 6×6 millimeter die has more than 460 million transistors. The silicon has been tested in the lab and is working, according to the research team.
The Piton architecture contains 25 tiles connected in 5×5 2D mesh topology. Each tile consists of a modified OpenSPARC T1 core (running at 1 GHz @ .9 volts), L1.5 cache, L2 cache, a floating-point unit (FPU), a Cache-Crossbar (CCX) arbiter and three NoC routers. An off-chip interface (Chip Bridge) extends the NoC and coherence protocol to support up to 8,000 chips per system (200,000 cores) with all cores being able to access memory. For further details, refer to the researchers Hot Chips paper.
Piton offers unique cache memory handling in that it can assign areas of the cache and specific cores to dedicated applications. Altogether, the researchers say their design decisions result in an efficiency gain of 29 percent per chip.
The Princeton researchers open sourced the Piton design in June 2015. OpenPiton is the first open source, general-purpose, multithreaded manycore processor, according to the team. The emergent open hardware trend also has support from Facebook’s Open Compute Project (at the rack level) and fabless startup Si-Five, which last month launched open source chip platforms based on the RISC-V ISA.
“We’re very pleased with all that we’ve achieved with Piton in an academic setting, where there are far fewer resources than at large, commercial chipmakers,” Wentzlaff said. “We’re also happy to give out our design to the world as open source, which has long been commonplace for software, but is almost never done for hardware.”
Photo source: David Wentzlaff, Department of Electrical Engineering, Princeton University