Comparing Memory Architectures: Shared vs. Message Passing in Cray T3E and IBM SP, Slides of Advanced Computer Architecture

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4: Distribute Memory Architecture

Cray T3E is a typical example of NUMA architecture

4: Distribute Memory Architecture

Cray T3E is a typical example of NUMA architecture which scales up to 1024 processors with 480 MB/sec. links

Here, the non-local references are accessed using communication requests generated automatically by the memory controller in the external I/Os

Here no hardware coherence mechanism is employed rather directory based cache- coherence protocols are used – We will discuss this in detail later

Message Passing Architecture

Programming Model

Message Passing Architecture

Note that the message passing is essentially NUMA but it is integrated at I/O devices vs. memory system

Here, the local memory is directly accessed, i.e., it directly accesses the private address space (e.g., the processor P directly access the local address X; and

Communication takes place via explicit message passing, i.e., via send/receive

Message Passing Architecture

Send and receive is memory-memory copy, where each supplies local address, AND does pair-wise synchronization The synchronization is achieved as follows: receive wait for send when

• send completes
• buffer free and
• request accepted

Message Passing Architecture Communication Model The high-level block diagram for complete computer as a building block, similar to the distributed memory spared address space is shown here to describe the communication abstraction

Message Passing Architecture Communication Model

IBM SP: Message Passing Machine

Made out of essentially complete RS6000 workstations

Network interface integrated in I/O bus

Bandwidth is limited by I/O bus

Summary

Today we have explored how further improvement in computer performance can be accomplished using Parallel Processing Architectures

Parallel Architecture is a collection of processing elements that cooperate and communicate to solve larger problems fast

Then we described the four categories of Parallel Architecture as: SISD, SIMD, MISD and MIMD architecture

Summary

These models present sharing of address space and message passing in parallel architecture

The advantages of Shared-Memory

Communication model are as follows:

• Ease of programming when communication patterns are complex or vary dynamically during execution

Summary

• Lower communication overhead,

better use of BW for small items

• HW-controlled caching to reduce

remote comm. by caching of all

data, both shared and private

The advantages of message passing

communication model are as follows:

Thanks

and

Allah Hafiz