[Tim Shattuck, 2006][1] Performance / Watt: The New Server Focus Improving Performance / Watt For Modern Processors Tim Shattuck April 19, 2006 From the Paper by James Laudon Computer Architecture News, Volume 33, Number 4, September 2005

[Tim Shattuck, 2006][2] At Issue: Power Hungry Servers Increasing Costs to Power Hardware Wastes Limited Resources

[Tim Shattuck, 2006][3] Three Trends High power consumption to performance gains ratio Hardware costs account for a smaller percentage of Total Cost of Ownership (TCO) Energy costs are rising These trends are expected to make power the dominant factor in calculating TCO within five years.

[Tim Shattuck, 2006][4] Niagra Optimizations Simple Clock gating Pipelines More complex Hardware support for multithreading

[Tim Shattuck, 2006][5] Simple Optimizations Clock gating Don't power idle parts of the chip Shorter, medium-length pipelines Fewer registers, transistors between stages Less power wasted on (failed) speculation Allow for more cores / chip

[Tim Shattuck, 2006][6] More Optimizations Hardware Multithreading Keep on-chip resources busy Deals with high cache miss rates Boosts performance / Watt Increases throughput of threads Increases power consumption only slightly Increases size of the die 4 - 7% per thread

[Tim Shattuck, 2006][7] Cores / Die Fewer complex cores More simple cores Individual thread completion Aggregate thread throughput Simpler cores tend to have better performance / Watt ratios

[Tim Shattuck, 2006][8] Sufficient Cache and Memory Bandwidth Necessary to keep threads busy Sun's Niagra: Cores connected to L2 cache by a crossbar switch Cache bandwidth of 76.8 GB/s Four memory controllers directly connected to DDR2 SDRAM memory unit (200 Mhz) Raw memory bandwidth of 25.6 GB/s Controllers can reorder accesses to favor reads over writes.

[Tim Shattuck, 2006][9] Testing SPEC JBB 2000 Java server side business logic TPC-C, TPC-W Transactional processing tests XML Test Sun's multithreaded processing test. Result: Scalar processors with moderate pipelines and thread support outperformed superscalar processors.

[Tim Shattuck, 2006][10] Case Studies Sun's Niagra 8 cores, 4 threads each Scalar cores Tries to maximize performance / Watt Intel's Pentium Extreme Edition 2 cores, 2 threads each Superscalar cores Tries to maximize performance

[Tim Shattuck, 2006][11] Case Studies (II) - Results FeatureNiagraPentium Extreme Edition Clock Speed1.2 Ghz3.2 Ghz Pipeline Depth6 stages31 stages Number of Cores82 Number of Threads324 L2 Bandwidth76.8 GB/s~180 GB/s Memory Bandwidth25.6 GB/s6.4 GB/s Transistor Count279 Million230 Million Power72 W130 W

[Tim Shattuck, 2006][12] Simple Core Limitations Lower single thread performance Amplified by lower instruction level parallelism Keeping a large number of threads busy may become difficult Hot locks – threaded applications may not scale very well

[Tim Shattuck, 2006][13] Future Directions Use multithreading to enhance single threaded applications Run-ahead execution – allows out of order execution with only a modest amount of hardware Software control of power consumption Dynamic adjustments to voltage and frequency to tune power consumption Control of non-processing devices' (disk, memory systems) power consumption

[Tim Shattuck, 2006][14] Conclusion Invest in a Niagra today!