Single-Chip Multi-Processors (CMP) PRADEEP DANDAMUDI 1 ELEC , Fall 08

Microprocessor Methods 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 ELEC , 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 ELEC , 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 ELEC , Fall 08

Superscalar pipeline 5 ELEC , 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 ELEC , 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 ELEC , 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 ELEC , 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 ELEC , 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 ELEC , Fall 08

Single chip Multiprocessor architecture 11 ELEC , 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 ELEC , Fall 08

13 ELEC , Fall 08

14 ELEC , 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 ELEC , Fall 08

References 07CAC003 L Hammond, BA Nayfeh, K Olukotun, “A Single-Chip Multiprocessor,” IEEE, Sept 1997.A Single-Chip Multiprocessor essors.pdf Chip Multiprocessor (CMP) Architectures,web.cecs.pdx.edu/~mperkows/CAPSTONES/DSP1/ELG6163_Burton.ppt en.wikipedia.org/wiki/ 16 ELEC , Fall 08