forked from Imagelibrary/rtems
38b59a6d30
The current implementation of task migration in RTEMS has some implications with respect to the interrupt latency. It is crucial to preserve the system invariant that a task can execute on at most one processor in the system at a time. This is accomplished with a boolean indicator in the task context. The processor architecture specific low-level task context switch code will mark that a task context is no longer executing and waits that the heir context stopped execution before it restores the heir context and resumes execution of the heir task. So there is one point in time in which a processor is without a task. This is essential to avoid cyclic dependencies in case multiple tasks migrate at once. Otherwise some supervising entity is necessary to prevent life-locks. Such a global supervisor would lead to scalability problems so this approach is not used. Currently the thread dispatch is performed with interrupts disabled. So in case the heir task is currently executing on another processor then this prolongs the time of disabled interrupts since one processor has to wait for another processor to make progress. It is difficult to avoid this issue with the interrupt latency since interrupts normally store the context of the interrupted task on its stack. In case a task is marked as not executing we must not use its task stack to store such an interrupt context. We cannot use the heir stack before it stopped execution on another processor. So if we enable interrupts during this transition we have to provide an alternative task independent stack for this time frame. This issue needs further investigation.
Tools Required ============== The following tools are used in the production of this documentation: TeX texi2html 1.82 texinfo-tex 4.13a texi2html will be deprecated in the upcomine texinfo release. At that point, we will need to provide support for texi2any.pl as an alternative means to produce html output. This was used by the authors to generate the directory tree figure in the texinfo printed version: tree (from the CTAN Archives -- see http://jasper.ora.com/ctan.html) Changing the Version Number and Timestamp ========================================= RTEMS Version number is in configure.in. Edit that file and run bootstrap. Documentation date is in common/setup.texi.in and also must be modified by hand. bootstrap does not have to be run after modifying this file. Making the Documentation ======================== cd rtems-XXX/doc ../bootstrap ./configure --enable-maintainer-mode make all make install Cleaning ======== make clean make distclean make maintainer-clean Making a Source Distribution ============================ This generates a rtems-<version>.tar.gz in the toplevel directory. Making a Preformatted Distribution ================================== Install and tar it up. :)