Dual Core Processing

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What is a dual core processor?

A dual-core processor combines twoindependent processors and their respective

caches and cache controllers onto a singlesilicon chip.

They fall into the architectural class of tightly-coupled multiprocessor.

IBMs POWER4 was the first dual coreprocessor. AMD, INTEL, Sun have since broughtout their own models.


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Why a dual core processor?

Microprocessor performance scaling has been sustained byincreasing clock frequency and instruction-level parallelism (ILP).However, these two factors are both reaching the point of

diminishing returns. Network-based applications, such as online transaction processing,

are rich in thread-level parallelism which require high computingthroughput to execute multiple threads/processes simultaneouslyrather than high single thread performance.

Power consumption is also critical.

The critical requirements for these types of applications are highcomputing throughput, high memory bandwidth, large addressingspace, high reliability, low power and low cost. To address theabove design targets, the optimum solution is an on-chip dual-core

processor.


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Architecture

The general architecture was as shown in slide 3.

Here I will explaining dual-core processor based on the UltraSPARCI/II micro-architecture.

It has a 1MB L2 cache, DDR-1 memory controller and symmetricmultiprocessor bus (JBus) interfaces.

This core provides an efficient performance per watt havingbalanced hardware complexity with 4-issue superscalar, 9-stagepipeline and in-order execution/out-of-order completion.

Predominantly static circuit design styles and the balanced H-treeclock distribution also contribute to achieving low power.

Typical power dissipation at 1.2GHz and 1.3V is 23Watts, which isthe lowest published figure for 64b server processors.


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Architecture contd

The memory controller supports up to 16GB of physicalmemory.

JBus controllers allow low-cost multiprocessing systemswith configurations of up to four-chips (eight threads).

The chip is fabricated in Texas Instruments' advanced0.13m CMOS process with 7 layers of Cu and a low-k

dielectric. The transistor count is 80M.


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Chip Block Diagram


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Applications and benefits

There are a number of categories of applications andmiddleware that can benefit from dual-core processors.

The following tables summarize the categories and

representative applications that should see significantbenefit, moderate benefit, or little benefit from a switchfrom single-core to dual-core processors.


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Table 2:The benefits for dual-core servers


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The benefits for dual-coreservers contd


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Table 3 :The benefits forworkstations.


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Performance Comparisons The given below are tests IBM performed with a

number of industry benchmarks to compare the fastestsingle- and dual-core Opteron processors available for

the e326 and the LS206. These benchmarks can be useful for comparing

processor performance under varying workloads.


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Linpack:Graph 1shows the results of

the Linpack benchmark


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Table 4compares published SPECint_rate2000and SPECfp_rate2000 scores for single-core LS20

servers versus dual-core LS20 and e326 servers.


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STREAM :Table 5compares results for single-core e326 and LS20 servers versus dual-core

servers.


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Hyper Threading Vs Dual Core Processing

or is it? In a single-core dual-threaded processor, each thread is

assigned its own set of registers. This makes theprocessor appear as two (virtual) processors.

But this rarely happens because those virtual processorsare still part of one physical processor, requiring thethreads to time-share common resources such asinteger units, floating-point units and cache.

The effective throughput is somewhat less than the

theoretical, with one thread waiting for the other torelease a resource. In addition, if the software stack islargely single-threaded, the second virtual processormay be idle much of the time, rendering its value moot.


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Hyper Threading Vs Dual Core Processingor is it? Contd.

With a dual-core dual-threaded processor, you actuallyhave two physical processors on one chip

Because each core has its own cache, registers and

other resources, there is less resource contention thanyou might see with a simple dual-threaded, single-coreprocessor.

Two separate single- or multithreaded programs can be

running simultaneously, for up to twice the throughputof a same-speed single-core processor


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Hyper Threading Vs Dual Core Processingor is it? Contd.

For hyper-threading its strength is also its weakness.

On the one hand, a deeply pipelined CPU is able to takecare of multiple actions within a processing cycle.

On the other hand, each and every operation will causethe CPU to go through most of these stages, which caneasily end up wasting valuable clock cycles.

To compensate in part, Intel implemented logic that can

provide a higher average utilization of the Pentium 4pipeline - which has grown to 31 stages with thecurrent Prescott architecture


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Drawbacks

The availability of Dual core processors.

The need for the software to be aware of dual corespresent.

Need for new motherboards for some of the newerprocessors in case of a upgrade.


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Future Trends

Beyond dual-core processors, there are examples ofchips with multiple cores. Such chips include networkprocessors which may have a large number of cores or

microengines that may operate independently ondifferent packet processing tasks within a networkingapplication.

One option is to widen the registers and/or the businterface of an existing processor architecture.

Widening the bus interface alone leads to superscalarprocessor architectures, and widening both usuallyrequires new programming models.

Other options include including multiple levels ofmemory cache, and developing system-on-a-chip

solutions.


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Conclusion

A server with one DC processor is much like a serverwith two SC processors in one respect. In order to seethe full benefits of dual-core processors, especially with

64-bit software, it is necessary to provide amplerequirements for the software.

Given the performance advantages of dual-coreprocessors, does this mean the end of single-coreprocessors? Eventually, yes

For now concurrency especially in the form ofsimultaneous multithreading(SMT) and dual-coreprocessors on the same die is the design seems toprovide the best performance per square millimeter of

silicon.


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References

A Dual-Core 64b UltraSPARC Microprocessor for DenseServer Applications

By Toshinari Takayanagi, Jinuk Luke Shin, Bruce Petrick, Jeffrey Suand Ana Sonia Leon, Sun Microsystems, Inc.

The Benefits of Dual-Core Processors in High-PerformanceComputing

By Mark T. Chapman, IBM Systems and Technology Group

VIS Instruction Set Users Manual, Sun Microsystems, Inc.

HOT CHIPS 15SCALING THE SILICON MOUNTAIN, IEEE MICRO,MARCHAPRIL 2004

www.wikipedia.com, www.amd.com, www.intel.com,www.ibm.com, www.sun.com
http://www.wikipedia.com/http://www.amd.com/http://www.intel.com/http://www.ibm.com/http://www.sun.som/http://www.sun.som/http://www.ibm.com/http://www.intel.com/http://www.amd.com/http://www.wikipedia.com/


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