Separately, IBM pushed its z196 CPU to 5.2 GHz, about 18 percent above the previous 4.4 GHz z10 chip while maintaining similar thermal envelope. Frequency is key for getting top single-thread performance the mainframe class system requires.
"We think there is still room for future improvements, but frequency increases won't go on forever," said Jim Warnock, a senior IBM engineer.
The multichip modules used in IBM's z-Series servers include six CPUs and two L4 cache chips and consume a whopping 1,800 Watts. The processors themselves have a 260 Watt power budget, but could get more headroom if new MCM materials can be found.
"We are the last of the high-end processors still pushing higher frequency," said Warnock.
To get the speed boost IBM moved the design from 65 to 45nm SOI process technology. It also made extensive use of embedded DRAM for memory and capacitors. IBM also added out-of-order execution to the chip, gaining a 40 percent total performance improvement from all the new techniques.
IBM conducted extensive power analysis of the design, calculating dynamic and leakage power with various workloads. Resulting power and thermal budgets were applied to work from the planning to the physical implementation design of the part.
Designers used an extensive set of tools to optimize frequency tuning. They included delaying the master clock and local clock pulse width and timing controls.
In a separate paper, IBM described 14-bit cache hit logic tied to SRAM cache blocks used to enable the high frequencies on eight critical paths.
1. Godson eyes petaflops
2. IBM hits 5.2 GHz
3. AMD Bulldozer, Intel server CPUs