CSCI 6380 More Multiprocessors

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CSCI 6380 More Multiprocessors

Coherency & MP Performance

Performance of Symmetric Shared-Memory Multiprocessors

Coherency Misses

Example: True v. False Sharing v. Hit?

MP Performance 4 Processor Commercial Workload: OLTP, Decision Support (Database), Search Engine

MP Performance 2MB Cache Commercial Workload: OLTP, Decision Support (Database), Search Engine

A Cache Coherent System Must:

Bus-based Coherence

Scalable Approach: Directories

Basic Operation of Directory

Directory Protocol

Directory Protocol Messages (Fig 4.22)

State Transition Diagram for One Cache Block in Directory Based System

CPU -Cache State Machine

State Transition Diagram for Directory

Directory State Machine

Implementing a Directory

Basic Directory Transactions

Example Directory Protocol (1st Read)

Example Directory Protocol (Read Share)

Example Directory Protocol (Wr to shared)

Example Directory Protocol (Wr to Ex)

Implementing Directories

A Popular Middle Ground

Synchronization

Uninterruptable Instruction to Fetch and Update Memory

User Level Synchronization—Operation Using this Primitive

Another MP Issue: Memory Consistency Models

Memory Consistency Model

Relaxed Consistency Models: The Basics

Mark Hill observation

Example—Sun Niagara

T1 (“Niagara”)

T1 Architecture

T1 Fine-Grained Multithreading

Memory, Clock, Power

Miss Rates: L2 Cache Size, Block Size

Miss Latency: L2 Cache Size, Block Size

CPI Breakdown of Performance

Not Ready Breakdown

Performance: Benchmarks + Sun Marketing

HP marketing view of T1 Niagara

Microprocessor Comparison

Performance Relative to Pentium D

Performance/mm2, Performance/Watt

Cross Cutting Issues: Performance Measurement of Parallel Processors

Fallacy: Amdahl’s Law doesn’t apply to parallel computers

Fallacy: Linear speedups are needed to make multiprocessors cost-effective

Fallacy: Scalability is almost free

Pitfall: Not developing SW to take advantage of (or optimize for) multiprocessor architecture

Answers to 1995 Questions about Parallelism

Cautionary Tale

And in Conclusion …

Author: Doug Hoffman

E-mail: hoffman@dlhoffman.com

Homepage: http://www.dlhoffman.com/classnotes/csci6380-s08