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UltraSPARC T1
UltraSPARC T1
By LinuxHPC.org and Cluster Resources
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Sun Microsystems' UltraSPARC T1 microprocessor, known until its 14 November 2005 announcement by its development codename "Niagara" , is a multithreading, multicore CPU. Designed to lower the energy consumption of server computers, the CPU uses typically 72 W of power at 1.2 GHz.
The T1 is a derivative of the UltraSPARC series of microprocessors. It is Sun's first multicore processor with multithreading. The processor is available with four, six or eight CPU cores, each core able to handle four threads concurrently. Thus the processor is capable of processing up to 32 threads concurrently.
Similar to how high-end Sun SMP systems work, the UltraSPARC T1 can be partitioned. Thus, several cores can be partitioned for running a single or group of processes and/or threads, whilst the other cores deal with the rest of the processes on the system.
Cores
The UltraSPARC T1 was designed from scratch as a multi-threaded, special-purpose processor, and thus introduces a whole new architecture for obtaining high performance. Rather than try to make each core as intelligent and optimized as they can, Sun's goal was to run as many concurrent threads as possible, and maximize utilization of each core's pipeline.
This approach appears to have worked well. Current benchmarks suggest each core in the UltraSPARC T1 is more powerful than the circa 2001, single-core, single-threaded UltraSPARC III, and executes the full SPARC v9 instruction set.
The T1's cores are less complex than those of current high end processors in order to allow 8 cores to fit on the same die. The cores do not feature out-of-order execution, or a sizable amount of cache. Single-thread processors depend heavily on large caches for their performance because cache misses result in a wait while the data is fetched from main memory. By making the cache larger the probability of a cache miss is reduced, but the impact of a miss is still the same.
The T1 cores largely side-step the issue of cache misses by multithreading. When a cache miss occurs, the core switches to another thread (assuming one is available) while the data is fetched into cache in the background. This may make each thread slower, but the overall throughput (and utilization) of each core is much higher. It also means that much of the impact of cache misses is removed, and the T1 can maintain high throughput with a smaller amount of cache. The cache no longer needs to be large enough to hold all or most of the "working set", just the recent cache misses of each thread.
"Rock"
The UltraSPARC T1 is designed for single CPU systems only and is not capable of SMP. Future Sun CMT UltraSPARC processors, such as Rock, will support multiple chip server architectures. The Rock processor targets traditional data facing workloads such as databases. As such, it is seen as the logical follow-on to Sun's SMP processors such as UltraSPARC III.
Rock also targets floating point workloads, unlike UltraSPARC T1. Sun has publicly disclosed a feature in the Rock processor called "Hardware Scout", which uses multithreaded hardware to perform prefetching.
Rock is not a successor to UltraSPARC T1. Sun has publicly disclosed plans for a Niagara2 processor which will target the same network facing workloads as UltraSPARC T1.
UltraSPARC T2
The UltraSPARC T2 will support eight threads per core, and each core will have its own FPU.
Open-source
On March 21, 2006, Sun made the UltraSPARC T1 source code available under the GNU General Public License (GPL).
- Verilog source code of the UltraSPARC T1 design;
- Verification suite and simulation models;
- ISA specification (UltraSPARC Architecture 2005);
- The Solaris 10 OS simulation images.