unsafe-problem

von vi V.

Why is this unsafe?

Process 0	Process 1
Send(1)	Send(0)
Recv(1)	Recv(0)

depends on availability of buffers in which to store data sent until can be received

What are some solutions for the unsafe problem=

Solution: make operation more carefully

Process 0	Process 1
Send(1)	Send(0)
Recv(1)	Recv(0)

Process 0	Process 1
Send(1)	Recv(0)
Recv(1)	Send(0)

Solution: Supply receive buffer and send buffer at same time

Process 0	Process 1
Send(1)	Send(0)
Recv(1)	Recv(0)

Process 0	Process 1
Sendrecv(1)	Sendrecv(0)

Solution: supply own space as buffer for send

Process 0	Process 1
Send(1)	Send(0)
Recv(1)	Recv(0)

Process 0	Process 1
Bsend(1)	Bsend(0)
Recv(1)	Recv(0)

Solution: Use non-blocking operations

Process 0	Process 1
Send(1)	Send(0)
Recv(1)	Recv(0)

What are some optimizations for Process Mapping?

4x8 decomposition btw MPI processes

machine with 4 nodes, each with 8 cores

What is difference btw Message-Passing and Remote memory access RMA?

Message-Passing = two-sided semantics, cooperative model

Operations: (e.g MPI_Send(), MPI_Recv(), MPI_Bcast())

Remote memory access RMA = one-sided semantic, only initiator makes procedure call

Operations: (e.g MPI_Put(), MPI_Get())

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