Clustered/partitioned scheduling helps to control the worst-case
latencies in the system. The goal is to reduce the amount of shared
state in the system and thus prevention of lock contention. Modern
multi-processor systems tend to have several layers of data and
instruction caches. With clustered/partitioned scheduling it is
possible to honour the cache topology of a system and thus avoid
expensive cache synchronization traffic.
We have clustered scheduling in case the set of processors of a system
is partitioned into non-empty pairwise-disjoint subsets. These subsets
are called clusters. Clusters with a cardinality of one are partitions.
Each cluster is owned by exactly one scheduler instance.
Do not allocate the scheduler control structures from the workspace.
This is a preparation step for configuration of clustered/partitioned
schedulers on SMP.
Rename rtems_smp_get_current_processor() in
rtems_get_current_processor(). Make rtems_get_current_processor() a
function in uni-processor configurations to enable ABI compatibility
with SMP configurations.
Rename rtems_smp_get_processor_count() in rtems_get_processor_count().
Make rtems_get_processor_count() a function in uni-processor
configurations to enable ABI compatibility with SMP configurations.
This simplifies the RTEMS initialization and helps to avoid a memory
overhead. The workspace demands of the IO manager were not included in
the <rtems/confdefs.h> workspace size estimate. This is also fixed as a
side-effect.
Update documentation and move "Specifying Application Defined Device
Driver Table" to the section end. This sub-section is not that
important for the user. Mentioning this at the beginning may lead to
confusion.
Per task variables are inherently unsafe in SMP systems. This
patch disables them from the build and adds warnings in the
appropriate documentation and configuration sections.
Delete global variables _Priority_Major_bit_map and _Priority_Bit_map.
This makes it possible to use multiple priority scheduler instances for
example with clustered/partitioned scheduling on SMP.
Issue a fatal error in case a thread is deleted which still owns
resources (e.g. a binary semaphore with priority inheritance or ceiling
protocol). The resource count must be checked quite late since RTEMS
task variable destructors, POSIX key destructors, POSIX cleanup handler,
the Newlib thread termination extension or other thread termination
extensions may release resources. In this context it would be quite
difficult to return an error status to the caller.
An alternative would be to place threads with a non-zero resource count
not on the zombie chain. Thus we have a resource leak instead of a
fatal error. The terminator thread can see this error if we return an
RTEMS_RESOURCE_IN_USE status for the rtems_task_delete() for example.
Add _Thread_queue_Extract_with_return_code(). On SMP this sequence in
_Thread_queue_Process_timeout() was broken:
[...]
/*
* After we enable interrupts here, a lot may happen in the
* meantime, e.g. nested interrupts may release the resource that
* times out here. So we enter _Thread_queue_Extract()
* speculatively. Inside this function we check the actual status
* under ISR disable protection. This ensures that exactly one
* executing context performs the extract operation (other parties
* may call _Thread_queue_Dequeue()). If this context won, then
* we have a timeout.
*
* We can use the_thread_queue pointer here even if
* the_thread->Wait.queue is already set to NULL since the extract
* operation will only use the thread queue discipline to select
* the right extract operation. The timeout status is set during
* thread queue initialization.
*/
we_did_it = _Thread_queue_Extract( the_thread_queue, the_thread );
if ( we_did_it ) {
the_thread->Wait.return_code = the_thread_queue->timeout_status;
}
[...]
In case _Thread_queue_Extract() successfully extracted a thread, then
this thread may start execution on a remote processor immediately and
read the the_thread->Wait.return_code before we update it here with the
timeout status. Thus it observes a successful operation even if it
timed out.
The holder field is enough to determine if a mutex is locked or not.
This leads also to better error status codes in case a
rtems_semaphore_release() is done for a mutex without having the
ownership.
The thread deletion is now supported on SMP.
This change fixes the following PRs:
PR1814: SMP race condition between stack free and dispatch
PR2035: psxcancel reveals NULL pointer access in _Thread_queue_Extract()
The POSIX cleanup handler are now called in the right context (should be
called in the context of the terminating thread).
http://pubs.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_09.html
Add a user extension the reflects a thread termination event. This is
used to reclaim the Newlib reentrancy structure (may use file
operations), the POSIX cleanup handlers and the POSIX key destructors.
Split sp09 screen 1 into new test sptask_err04.
Split sp09 screen 2 into new tests sptask__err02 and spclock_err01,
as well as moving one verification into sptimer_err01.
