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Questions and Answers
What is the purpose of message passing in MPI?
To generate synchronism, i.e., dependency among tasks communicating with each other.
What is the difference between MPI_Comm_size and MPI_Comm_rank?
MPI_Comm_size returns the number of processes, while MPI_Comm_rank returns the rank of the current process.
What is the purpose of MPI_Init function?
To introduce this process to the others.
What is the role of the master process in the given code?
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What is the purpose of MPI_Finalize function?
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What is the purpose of the MPI_Send function?
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What is the purpose of the MPI_Recv function?
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How many processes are generated by the code in Listing 8.2?
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What is the significance of the MPI_COMM_WORLD argument in MPI functions?
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How does the code in Listing 8.2 demonstrate parallelism?
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Study Notes
Multiple Instruction, Multiple Data (MIMD) Systems
- MIMD architecture is related to multiprocessors, where different instructions can work on different data in parallel.
- Multiprocessors are computers consisting of tightly coupled processors, whose coordination and usage are controlled by a single operating system.
- Processors in a multiprocessor system share memory through a shared address space.
Memory Organization
- Multiple processors in a multiprocessor system can share:
- Cache memory, main memory, and I/O system
- Main memory and I/O system
- I/O system
- Nothing, communicating through networks
- Avoiding bottlenecks in the architecture is important, and the answer depends on project requirements.
- Multiprocessors can be classified in terms of their memory organization: symmetric (shared-memory) multiprocessors - SMP and distributed shared memory - DSM.
Symmetric (Shared-Memory) Multiprocessors - SMP
- SMP are centralized shared-memory multiprocessors with approximately 32 cores or less.
- All processors have equal access to a single centralized memory, with uniform access time - UMA.
- SMP use large caches and many buses to avoid bottlenecks.
- Each processor has its own local caches, and the shared cache is accessed through a bus.
Distributed Shared Memory - DSM
- DSM organization counts on a larger number of processor cores (e.g., 16 to 64).
- Distributed memory is used to increase bandwidth and reduce access latency.
- Communication among processors becomes more complex, requiring more software effort to take advantage of increased memory bandwidth.
- I/O system is also distributed, and each node can be a small distributed system with centralized memory.
- DSM has nonuniform memory access - NUMA, i.e., access time depends on the location of a data word in memory.
Memory Architecture: UMA and NUMA
- SMP follows UMA, where processors share a single memory and have uniform access times to the centralized memory.
- DSM follows NUMA, where processors share the same address space but not necessarily the same physical memory.
Communication Models
- SMP Communication Model:
- Uses threads and fork-join model.
- Implicit communication through memory access.
- OpenMP is an application programming interface for SMP.
- DSM Communication Model:
- Uses message passing model.
- Explicit communication through message passing.
- MPI (Message Passing Interface) is a library project implementing a message passing interface.
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Description
Learn about MIMD systems, multiprocessors, and memory organization in computer architecture. Understand how multiple processors work together and share memory.
