Granularity (parallel computing)

In parallel computing, granularity (or grain size) of a task is a measure of the amount of work (or computation) which is performed by that task.^[1]

Another definition of granularity takes into account the communication overhead between multiple processors or processing elements. It defines granularity as the ratio of computation time to communication time, wherein computation time is the time required to perform the computation of a task and communication time is the time required to exchange data between processors.^[2]

If $T comp$ is the computation time and $T comm$ denotes the communication time, then the granularity $G$ of a task can be calculated as:^[2]

G={\frac {T_{\mathrm {comp} }}{T_{\mathrm {comm} }}}

Granularity is usually measured in terms of the number of instructions which are executed in a particular task.^[1] Alternately, granularity can also be specified in terms of the execution time of a program, combining the computation time and communication time.^[1]

^ ^a ^b ^c Hwang, Kai (1992). Advanced Computer Architecture: Parallelism, Scalability, Programmability (1st ed.). McGraw-Hill Higher Education. ISBN 978-0070316225.
^ ^a ^b Kwiatkowski, Jan (9 September 2001). "Evaluation of Parallel Programs by Measurement of Its Granularity". Parallel Processing and Applied Mathematics. Lecture Notes in Computer Science. Vol. 2328. pp. 145–153. doi:10.1007/3-540-48086-2_16. ISBN 9783540437925. ISBN 9783540480860.

[hwang-1] Hwang, Kai (1992). Advanced Computer Architecture: Parallelism, Scalability, Programmability (1st ed.). McGraw-Hill Higher Education. ISBN 978-0070316225.

[Kwiatkowski-2] Kwiatkowski, Jan (9 September 2001). "Evaluation of Parallel Programs by Measurement of Its Granularity". Parallel Processing and Applied Mathematics. Lecture Notes in Computer Science. Vol. 2328. pp. 145–153. doi:10.1007/3-540-48086-2_16. ISBN 9783540437925. ISBN 9783540480860.

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