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37 lines
1.6 KiB
TeX
37 lines
1.6 KiB
TeX
\section{Task Affinity}
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\label{sec: task_affinity}
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\index{affinity!task affinity}
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\index{affinity!affinity clause@\code{affinity} clause}
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\index{clauses!affinity@\code{affinity}}
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\index{affinity clause@\code{affinity} clause}
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The next example illustrates the use of the \code{affinity}
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clause with a \code{task} construct.
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The variables in the \code{affinity} clause provide a
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hint to the runtime that the task should execute
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"close" to the physical storage location of the variables. For example,
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on a two-socket platform with a local memory component
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close to each processor socket, the runtime will attempt to
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schedule the task execution on the socket where the storage is located.
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Because the C/C++ code employs a pointer, an array section is used in
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the \code{affinity} clause.
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Fortran code can use an array reference to specify the storage, as
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shown here.
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Note, in the second task of the C/C++ code the \plc{B} pointer is declared
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shared. Otherwise, by default, it would be firstprivate since it is a local
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variable, and would probably be saved for the second task before being assigned
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a storage address by the first task. Also, one might think it reasonable to use
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the \code{affinity} clause \plc{affinity(B[:N])} on the second \code{task} construct.
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However, the storage behind \plc{B} is created in the first task, and the
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array section reference may not be valid when the second task is generated.
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The use of the \plc{A} array is sufficient for this case, because one
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would expect the storage for \plc{A} and \plc{B} would be physically "close"
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(as provided by the hint in the first task).
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\cexample[5.0]{affinity}{6}
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\ffreeexample[5.0]{affinity}{6}
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