[Tim Shattuck, 2006] [1]

Performance / Watt:The New Server Focus

Improving Performance / WattFor Modern Processors

Tim Shattuck <timshattuck@gmail.com>April 19, 2006

From the Paper by James Laudon <james.laudon@sun.com>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

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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

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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.

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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

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Case Studies (II) - Results

Feature Niagra Pentium Extreme EditionClock Speed 1.2 Ghz 3.2 GhzPipeline Depth 6 stages 31 stagesNumber of Cores 8 2Number of Threads 32 4L2 Bandwidth 76.8 GB/s ~180 GB/sMemory Bandwidth 25.6 GB/s 6.4 GB/sTransistor Count 279 Million 230 Million

Power 72 W 130 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

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Conclusion

Invest in a Niagra today!