Differences between version 6 and revision by previous author of SymmetricMultiProcessing.
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| Newer page: | version 6 | Last edited on Sunday, April 18, 2004 2:46:27 am | by StuartYeates | Revert |
| Older page: | version 5 | Last edited on Friday, April 16, 2004 7:32:29 am | by AristotlePagaltzis | Revert |
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A system with multiple identical [CPU]s having equal access to memory and to the [IO] subsytem(s). Contrast [NUMA] and AsymmetricMultiProcessing.
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-''StuartYeates writes that they may be only nearly identical. However, such setups are extremly rare to the point of irrelevance. In practice, all [SMP] systems run with setups such as dual-Opteron, quad-Xeon, dual-PowerPC, or others, where the [CPU]s are perfectly identical.'' --AristotlePagaltzis
It is an accepted rule of thumb that due to the InterProcessCommunication "friction" required to synchronize tasks across [CPU]s, each additional [CPU] contributes about 1/6 less performance than the previous one. As a result, fitting more than four [CPU]s in a machine tends to cost heaps of money with surprisingly little to show for it.
On the OperatingSystem level, there is a wide span for the degree of symmetry expressed. On a fully symmetric system, any [CPU] may run any userland process, any kernel process, and any interrupt handler. This is rare in practice due to limitations in various platforms -- most of the time, the interrupt handler can only be run by the first [CPU]. In simpler [OperatingSystem]s, this is also the only [CPU] that may kernel tasks. In yet simpler system designs, even user processes are assigned to a fixed [CPU] and cannot move among [CPU]s.
