Editing DragonFly BSD (section)

==== Threading ====
As support for multiple [[instruction set architecture]]s complicates [[symmetric multiprocessing]] (SMP) support,<ref name="behind-dfbsd" /> DragonFly BSD now limits its support to the [[x86-64]] platform.<ref name="osnews-mp-improved" /> DragonFly originally ran on the [[x86]] architecture, however as of version 4.0 it is no longer supported. Since version 1.10, DragonFly supports 1:1 userland threading (one kernel thread per userland thread),<ref name="luciani_dcbsdcon2009" /> which is regarded as a relatively simple solution that is also easy to maintain.<ref name="unix-for-clusters" /> Inherited from FreeBSD, DragonFly also supports multi-threading.<ref name="paying-off-already" />

In DragonFly, each [[Central processing unit|CPU]] has its own thread scheduler. Upon creation, threads are assigned to processors and are never preemptively switched from one processor to another; they are only migrated by the passing of an [[inter-processor interrupt]] (IPI) message between the CPUs involved. Inter-processor thread scheduling is also accomplished by sending asynchronous IPI messages. One advantage to this clean compartmentalization of the threading subsystem is that the processors' on-board [[CPU cache|caches]] in [[symmetric multiprocessor system]]s do not contain duplicated data, allowing for higher performance by giving each processor in the system the ability to use its own cache to store different things to work on.<ref name="unix-for-clusters" />

The [[Light Weight Kernel Threads|''LWKT'']] subsystem is being employed to partition work among multiple kernel threads (for example in the networking code there is one thread per protocol per processor), reducing competition by removing the need to share certain resources among various kernel tasks.<ref name="behind-dfbsd" />