Penguin
Blame: SymmetricMultiProcessing
EditPageHistoryDiffInfoLikePages
Annotated edit history of SymmetricMultiProcessing version 7, including all changes. View license author blame.
Rev Author # Line
7 AristotlePagaltzis 1 A system with multiple identical [CPU]s having equal access to memory and to the [I/O] subsytem(s). Contrast [NUMA] and AsymmetricMultiProcessing.
5 AristotlePagaltzis 2
4 StuartYeates 3 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.
4
7 AristotlePagaltzis 5 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.
4 StuartYeates 6
7 In practice, a less symmetric system OperatingSystem design may not be a drawback. It is desirable to tie processes to a certain [CPU] as long the system load is evenly distributed among [CPU]s, because this maximizes the efficiency of [CPU] caches. Even in a completely symmetric system, an intelligently written scheduler will take this into account and try not to shuffle tasks around needlessly.
8
7 AristotlePagaltzis 9 Applications have to be explicitly designed to exploit the additional processing power available in an [SMP] system. This is not often the case. It only commonly applies to multithreaded applications, which are common in the [Java] world where the [GUI], GarbageCollection, and application logic will often run on sepreate [CPU]s. (What else can you do when all your [I/O] is blocking? At least there are nonblocking [I/O] classes in more recent [Java] versions, but of course they add yet another layer to the already byzantine library.)

PHP Warning

lib/blame.php:177: Warning: Invalid argument supplied for foreach()