cc_staff
30
edits
OpenMP: Difference between revisions
Jump to navigation
Jump to search
no edit summary
No edit summary |
No edit summary |
||
| Line 4: | Line 4: | ||
OpenMP allows for the rapid development of fine-grained parallel applications on a multicore machine while staying close to the serial code. Although there is only one program instance running, it can execute multiple subtasks in parallel. Directives inserted into the program control the parallel execution and allow for the management of the computations' distribution between the subtasks. The beauty of these directives is that they are usually non-intrusive and the compiler that does not support them can still compile the program and the user can run it, serially of course, as usual. | OpenMP allows for the rapid development of fine-grained parallel applications on a multicore machine while staying close to the serial code. Although there is only one program instance running, it can execute multiple subtasks in parallel. Directives inserted into the program control the parallel execution and allow for the management of the computations' distribution between the subtasks. The beauty of these directives is that they are usually non-intrusive and the compiler that does not support them can still compile the program and the user can run it, serially of course, as usual. | ||
The OpenMP interface relies on the notion of threads, a well-known concept in the Operating Systems realm. A thread is a bit like a light process or a "virtual processor, operating serially", and can formally be defined as the smallest unit of work/processing that can be scheduled by an Operating System. From a programmer's point of view, if there are five threads, then that corresponds virtually to five cores that can do a computation in parallel. It is important to understand that the number of threads is independent of the number of physical cores within the computer. Two cores can, for example, run a program with ten threads. The operating system decides how to share the cores' time between threads. | The OpenMP interface relies on the notion of threads, a well-known concept in the Operating Systems realm. A thread is a bit like a light weight process or a "virtual processor, operating serially", and can formally be defined as the smallest unit of work/processing that can be scheduled by an Operating System. From a programmer's point of view, if there are five threads, then that corresponds virtually to five cores that can do a computation in parallel. It is important to understand that the number of threads is independent of the number of physical cores within the computer. Two cores can, for example, run a program with ten threads. The operating system decides how to share the cores' time between threads. | ||
Having said that, it is clear that if you have four available cores, you should use at least four threads to be able to profit from all the available computing power, as a thread can not be executed by two processors at the same time. It could be advantageous, in certain cases, to use more threads than the number of available cores. Using too many threads is not recommended, however. | Having said that, it is clear that if you have four available cores, you should use at least four threads to be able to profit from all the available computing power, as a thread can not be executed by two processors at the same time. It could be advantageous, in certain cases, to use more threads than the number of available cores. Using too many threads is not recommended, however. | ||