Single-Chip Multi-Processors (CMP)

PRADEEP DANDAMUDI

1

ELEC6200-001, Fall 08

MicroprocessorMethods To Increase Performance:

• The number of transistors available has a huge effect on the performance of a processor.

• More transistors also allow for a technology called pipelining.

• Parallelism

2

ELEC6200-001, Fall 08

Parallelism in Microprocessors• Pipelining is most prevalent

▫ Used in everything▫ Even microcontrollers▫ Decreases cycle time▫ Allows up to 1 instruction per cycle (IPC)▫ No programming changes▫ Some Pentium 4s have more than 30 stages!

• Parallelism classifications: Instruction level Loop level Thread level - Future trend Process level - Future trend

3

ELEC6200-001, Fall 08

Instruction Level Parallelism (ILP)• Competing technology - Superscalar

• Executing multiple instruction in the same clock cycle.

• Dynamic scheduling-ability to execute out of program order.

• Single processor

• Replace ALU with multiple functional units

• Dispatch several instructions at once

4

ELEC6200-001, Fall 08

Superscalar pipeline

5

ELEC6200-001, Fall 08

Competing technologies

• Simultaneous Multi Threading▫ Simultaneous Multi threading architecture is similar to that of

the superscalar.▫ SMT processors support wide superscalar processors with

hardware, to execute instructions from multiple thread concurrently.

• Out-of-Order Execution▫ Where instructions execute in any order that does not violate

data dependencies.▫ Note that this technique is independent of both pipelining and

superscalar

6

ELEC6200-001, Fall 08

Centralized architecture • Disadvantages of centralized architectures such as SMT

and Superscalars are:

- Area increases quadratically with core’s complexity.

- Increase in cycle time – interconnect delays. Delay with wires dominate delay of critical path of CPU. Possible to make simpler clusters, but results in deeper pipeline and increase in branch misprediction penalty.

- Design verification cost high, due to complexity and single processor

- Large demand on memory system.

7

ELEC6200-001, Fall 08

Why Multiprocessor Systems?• Single-core microprocessor performance increases are

beginning to slow [1] due to:▫ Increasing power consumption (>100 W)▫ Increasing heat dissipation▫ Diminishing performance gains from ILP & TLP

• As a result manufactures are turning to a multi-core microprocessor approach▫ Multiple smaller energy efficient processing cores are

integrated onto a single chip▫ Improves overall performance by performing more work

concurrently▫ The latencies associated with chip-to-chip communication

disappear, Shared data structures are much less of a problem.

8

ELEC6200-001, Fall 08

Case for single chip multiprocessors• Advances in the field of integrated chip processing.

- Gate density (More transistors per chip)

- Cost of wires

• Large uniprocessors are no longer scaling in performance, because it is only possible to extract a limited amount of parallelism from a typical instruction stream using conventional superscalar instruction issue techniques.

9

ELEC6200-001, Fall 08

CMP Architectures• Two general types of multi-core or chip

multiprocessor (CMP) architectures▫ Homogeneous CMPs – all processing elements

(PEs) are the same▫ Heterogeneous CMPs – comprised of different PEs

• Homogenous dual-core processors for PCs are now available from all major manufactures

• Heterogeneous CMPs are available in the form of multiprocessor systems-on-chips (MPSoCs)

10

ELEC6200-001, Fall 08

Single chip Multiprocessor architecture

11

ELEC6200-001, Fall 08

CMP Advantages• CMPs have several advantages over single processor

solutions▫ Energy and silicon area efficiency

By Incorporating smaller less complex cores onto a single chip

Dynamically switching between cores and powering down unused cores [5]

▫ Increased throughput performance by exploiting parallelism Multiple computing resources can take better

advantage of instruction, thread, and process level parallelism

12

ELEC6200-001, Fall 08

13

ELEC6200-001, Fall 08

14

ELEC6200-001, Fall 08

Summary• The CMP architecture is now the architecture

of choice for semiconductor manufactures

• CMPs are more area and energy efficient than single processor solutions

• CMPs achieve greater throughput than single processor solutions as more work can be done concurrently

• Custom multi-processor systems can now be designed and simulated from the ground up using software solutions from several companies

15

ELEC6200-001, Fall 08

References• http://www.morganclaypool.com/doi/abs/10.2200/

S00093ED1V01Y200707CAC003• L Hammond, BA Nayfeh, K Olukotun, “A Single-

Chip Multiprocessor,” IEEE, Sept 1997.http://occs.ieee.org/presentations/2007/070122_Jenks_ParallelMicroprocessors.pdf

• Chip Multiprocessor (CMP) Architectures ,web.cecs.pdx.edu/~mperkows/CAPSTONES/DSP1/ELG6163_Burton.ppt

• en.wikipedia.org/wiki/

16

ELEC6200-001, Fall 08