Sun Microsystems T5220, T5120 manual Memory Latency ComputeTime

13 The UltraSPARC T2 Processor with CoolThreads Technology Sun Microsystems, Inc.

simply increasing the number of cores would have gained additional throughput, but would have resulted in consuming extra die area, leaving no room for integrated components such as floating point processors.

The final UltraSPARC T2 processor design recognizes that memory latency is truly the bottleneck to improving performance. By increasing the number of threads supported by each core, and by further increasing network bandwidth, the UltraSPARC T2 is able provide approximately twice the throughput of the UltraSPARC T1 processor. Each UltraSPARC T2 processor provides up to eight cores, with each core able to switch between up to eight threads (64 threads per processor). In addition, each core provides two integer execution units, so that a single UltraSPARC core is capable of executing two threads at a time. Figure 4 provides a simplified high-level illustration of the thread model supported by an eight-core UltraSPARC T2 processor.

Thread 8
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Figure 4. A single eight-core UltraSPARC T2 processor supports up to 64 threads, with up to two threads running in each core simultaneously