1. Niagara: a 32-Way Multithreaded SPARC Processor P. Kongetira, K. Aingaran, K.Olokotun Sun Microsystems Presented by Bogdan Romanescu

2. Goal • Commercial server applications: • High thread level parallelism (TLP) • Large numbers of parallel client requests • Low instruction level parallelism (ILP) • High cache miss rates • Many unpredictable branches • Frequent load-load dependencies • Power, cooling, and space are major concerns for data centers

3. Sun’s Solution • UltraSPARC T1 processor • “the highest-throughput and most eco-responsible processor ever created”® • Multicore • Fine-grain multithreading within core • Simple pipelines • Small L1 cache • Shared L2 • Metric: Performance/Watt

4. Architecture

5. Sparc pipe • UltraSPARC II style • Single issue 6 stage: F, S, D, E, M, W • Shared units: • L1 $ • TLB • X units • pipe registers • Hazards: • Data • Structural

6. Integer Register file • One register file / thread • SPARC window: in, out, local registers • Highly integrated cell structure to support 4 threads: • 8 windows of 32 locations / thread • 3 read ports + 2 write ports • Read/write: single cycle latency • 1 Active Window Cell (copy of the architectural set window)

7. Thread scheduling • Thread selection based on: • Previous long latency instruction in pipe • Instruction type • LRU status • Select & Fetch coupled

8. Memory • 16 KB 4 way set assoc. I$/ core • 8 KB 4 way set assoc. D$/ core • 3MB 12 way set assoc. L2 $ shared • 4 x 750KB independent banks • 2 cycle throughput, 8 cycle latency • Direct link to DRAM & Jbus • Manages cache coherence for the 8 cores • CAM based directory • Write through • allocate LD • no-allocate ST

9. Performance

10. “Home run“ ? • Relatively slow single-thread performance • Poor floating-point performance • Lack of software support ( Sun Fire T2000 does not support Linux or Windows) • Price • Concurrency counterattack • no place as a general-purpose computer running databases • small low-end market segment ? • Niagara II & The “Rock” – multiprocessor & enhanced single thread support

11. References • [1] P. Kongetira, et al, “A 32-Way Multithreaded SPARC Processor,” IEEE Micro, vol. 25, pp. 21-29, Mar., 2005. • [2] A. S. Leon, et al, “A Power-Efficient High-Throughput 32-Thread SPARC Processor”, ISSCC 2006 , SESSION 5 , PROCESSORS • [3] S. Chaudhry, S. Yip, P. Caprioli and M. Tremblay, “High Performance Throughput Computing” , IEEE Micro, vol. 25, Issue 3, 2005 • [4] http://opensparc.sunsource.net/nonav/opensparct1.html • [5] http://www.sun.com/processors/UltraSPARC-T1/features.xml • [6] http://www.sun.com/servers/coolthreads/t1000/benchmarks.jsp • [7] http://news.com.com/Sun+begins+Sparc+phase+of+server+overhaul/2163-1010_3-5983365.html • [8] http://h71028.www7.hp.com/ERC/cache/280124-0-0-0-121.html