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The embedded brains GmbH & Co. KG is the legal successor of embedded
brains GmbH.
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Updates #4625.
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Updates #3053.
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Simplify callers of _Scheduler_SMP_Schedule_highest_ready(). Move the node
state change and the extraction from scheduled into
_Scheduler_SMP_Schedule_highest_ready(). Move the idle thread release to the
caller which have more information about the presence of an idle thread.
Update #4531.
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This patch fixes an issue with the idle thread handling in the SMP
scheduler framework used for the MrsP locking protocol. The approach to
use a simple chain of unused idle threads is broken for schedulers which
support thread to processor affinity. The reason is that the thread to
processor affinity introduces another ordering indicator which may under
certain conditions lead to a reordering of idle threads in the scheduled
chain. This reordering is not propagated to the chain of unused idle
threads. This could lead to use an idle thread for a sticky scheduler
node which is already in use. This locks up the system in infinite
loops in the thread context switch procedure.
To fix this, the SMP scheduler implementations must now provide
callbacks to get and release an unused idle thread.
Update #4531.
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This patch fixes the following broken behaviour:
While a thread is scheduled on a helping scheduler, while it does not
own a MrsP semaphore, if it obtains a MrsP semaphore, then no
scheduler node using an idle thread and the ceiling priority of the
semaphore is unblocked for the home scheduler.
This could lead to priority inversion issues and is not in line
with the MrsP protocol.
Introduce two new scheduler operations which are only enabled if
RTEMS_SMP is defined. The operations are used to make the scheduler
node of the home scheduler sticky and to clean the sticky property.
This helps to keep the sticky handing out of the frequently used
priority update operation.
Close #4532.
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Use the extract from scheduled callback provided by the scheduler
implementation in the SMP scheduler framework.
Update #4531.
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The return value was unused. Remove it.
Update #4531.
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Use common phrases for the file brief descriptions.
Update #3706.
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Use the following variant which was already used by most source files:
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
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Update #3706
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Add extract from scheduled function to the _Scheduler_SMP_Block()
operation. This allows a scheduler implementation to do extra work in
case a scheduled node is blocked.
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Thread priority changes may append or prepend the thread to its priority
group on the scheduler ready queue. Previously, a separate priority
value and a prepend-it flag in the scheduler node were used to propagate
a priority change to the scheduler.
Now, use an append-it bit in the priority control and reduce the plain
priority value to 63 bits.
This change leads to a significant code size reduction (about 25%) of
the SMP schedulers. The negligible increase of the standard priority
scheduler is due to some additional shift operations
(SCHEDULER_PRIORITY_MAP() and SCHEDULER_PRIORITY_UNMAP()).
Before:
text filename
136 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimpleblock.o
464 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimplechangepriority.o
24 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimple.o
108 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimpleschedule.o
292 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimpleunblock.o
264 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimpleyield.o
text filename
280 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerpriorityblock.o
488 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerprioritychangepriority.o
200 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerpriority.o
164 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerpriorityschedule.o
328 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerpriorityunblock.o
200 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerpriorityyield.o
text filename
24112 arm-rtems5/c/imx7/cpukit/score/src/libscore_a-scheduleredfsmp.o
text filename
37204 sparc-rtems5/c/gr740/cpukit/score/src/libscore_a-scheduleredfsmp.o
text filename
42236 powerpc-rtems5/c/qoriq_e6500_32/cpukit/score/src/libscore_a-scheduleredfsmp.o
After:
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136 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimpleblock.o
272 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimplechangepriority.o
24 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimple.o
108 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimpleschedule.o
292 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimpleunblock.o
264 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulersimpleyield.o
text filename
280 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerpriorityblock.o
488 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerprioritychangepriority.o
208 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerpriority.o
164 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerpriorityschedule.o
332 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerpriorityunblock.o
200 sparc-rtems5/c/erc32/cpukit/score/src/libscore_a-schedulerpriorityyield.o
text filename
18860 arm-rtems5/c/imx7/cpukit/score/src/libscore_a-scheduleredfsmp.o
text filename
28520 sparc-rtems5/c/gr740/cpukit/score/src/libscore_a-scheduleredfsmp.o
text filename
32664 powerpc-rtems5/c/qoriq_e6500_32/cpukit/score/src/libscore_a-scheduleredfsmp.o
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Update #3059.
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Only register ask for help requests in the scheduler unblock and yield
operations. The actual ask for help operation is carried out during
_Thread_Do_dispatch() on a processor related to the thread. This yields
a better separation of scheduler instances. A thread of one scheduler
instance should not be forced to carry out too much work for threads on
other scheduler instances.
Update #2556.
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Update #2797.
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Update #2556.
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Remove unused return status.
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Update #2556.
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Changed for consistency with other scheduler operations.
Update #2556.
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Changed for consistency with other scheduler operations.
Update #2556.
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Changed for consistency with other scheduler operations.
Update #2556.
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This enables to call this scheduler operation for all scheduler nodes
available to a thread.
Update #2556.
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Rename the scheduler ask for help stuff since this will be replaced step
by step with a second generation of the scheduler helping protocol.
Keep the old one for now in parallel to reduce the patch set sizes.
Update #2556.
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Add priority nodes which contribute to the overall thread priority.
The actual priority of a thread is now an aggregation of priority nodes.
The thread priority aggregation for the home scheduler instance of a
thread consists of at least one priority node, which is normally the
real priority of the thread. The locking protocols (e.g. priority
ceiling and priority inheritance), rate-monotonic period objects and the
POSIX sporadic server add, change and remove priority nodes.
A thread changes its priority now immediately, e.g. priority changes are
not deferred until the thread releases its last resource.
Replace the _Thread_Change_priority() function with
* _Thread_Priority_perform_actions(),
* _Thread_Priority_add(),
* _Thread_Priority_remove(),
* _Thread_Priority_change(), and
* _Thread_Priority_update().
Update #2412.
Update #2556.
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Provide the scheduler node to initialize or destroy to the corresponding
operations. This makes it possible to have more than one scheduler node
per thread.
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The thread priority is manifest in two independent areas. One area is
the user visible thread priority along with a potential thread queue.
The other is the scheduler. Currently, a thread priority update via
_Thread_Change_priority() first updates the user visble thread priority
and the thread queue, then the scheduler is notified if necessary. The
priority is passed to the scheduler via a local variable. A generation
counter ensures that the scheduler discards out-of-date priorities.
This use of a local variable ties the update in these two areas close
together. For later enhancements and the OMIP locking protocol
implementation we need more flexibility. Add a thread priority
information block to Scheduler_Node and synchronize priority value
updates via a sequence lock on SMP configurations.
Update #2556.
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Use priority maximum of scheduler instance. This avoids a potential
memory corruption on SMP configurations.
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Do not extract the idle threads from the ready set so that there is
always a thread available for comparison.
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The following scheduler operations return a thread in need for help
- unblock,
- change priority, and
- yield.
A thread in need for help is a thread that encounters a scheduler state
change from scheduled to ready or a thread that cannot be scheduled in
an unblock operation. Such a thread can ask threads which depend on
resources owned by this thread for help.
Add a new ask for help scheduler operation. This operation is used by
_Scheduler_Ask_for_help() to help threads in need for help returned by
the operations mentioned above. This operation is also used by
_Scheduler_Thread_change_resource_root() in case the root of a resource
sub-tree changes. A use case is the ownership change of a resource.
In case it is not possible to schedule a thread in need for help, then
the corresponding scheduler node will be placed into the set of ready
scheduler nodes of the scheduler instance. Once a state change from
ready to scheduled happens for this scheduler node it may be used to
schedule the thread in need for help.
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Return a thread in need for help for the following scheduler operations
- unblock,
- change priority, and
- yield.
A thread in need for help is a thread that encounters a scheduler state
change from scheduled to ready or a thread that cannot be scheduled in
an unblock operation. Such a thread can ask threads which depend on
resources owned by this thread for help.
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This emphasizes that the scheduler node of a thread is returned and this
is not a function working with scheduler nodes like the other *_Node_*()
functions.
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Avoid copy and paste and set the scheduler node state in one place.
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Add a chain node to the scheduler node to decouple the thread and
scheduler nodes. It is now possible to enqueue a thread in a thread
wait queue and use its scheduler node at the same for other threads,
e.g. a resouce owner.
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This reduces the API to the minimum data structures to maximize the
re-usability.
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The _Scheduler_Yield() was called by the executing thread with thread
dispatching disabled and interrupts enabled. The rtems_task_suspend()
is explicitly allowed in ISRs:
http://rtems.org/onlinedocs/doc-current/share/rtems/html/c_user/Interrupt-Manager-Directives-Allowed-from-an-ISR.html#Interrupt-Manager-Directives-Allowed-from-an-ISR
Unlike the other scheduler operations the locking was performed inside
the operation. This lead to the following race condition. Suppose a
ISR suspends the executing thread right before the yield scheduler
operation. Now the executing thread is not longer in the set of ready
threads. The typical scheduler operations did not check the thread
state and will now extract the thread again and enqueue it. This
corrupted data structures.
Add _Thread_Yield() and do the scheduler yield operation with interrupts
disabled. This has a negligible effect on the interrupt latency.
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These functions are used only via the function pointers in the generic
SMP scheduler implementation. Provide them as static inline so that the
compiler can optimize more easily.
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This scheduler attempts to account for needed thread migrations caused
as a side-effect of a thread state, affinity, or priority change operation.
This scheduler has its own allocate_processor handler named
_Scheduler_SMP_Allocate_processor_exact() because
_Scheduler_SMP_Allocate_processor() attempts to prevent an executing
thread from moving off its current CPU without considering affinity.
Without this, the scheduler makes all the right decisions and then
they are discarded at the end.
==Side Effects of Adding This Scheduler==
Added Thread_Control * parameter to Scheduler_SMP_Get_highest_ready type
so methods looking for the highest ready thread can filter by the processor
on which the thread blocking resides. This allows affinity to be considered.
Simple Priority SMP and Priority SMP ignore this parameter.
+ Added get_lowest_scheduled argument to _Scheduler_SMP_Enqueue_ordered().
+ Added allocate_processor argument to the following methods:
- _Scheduler_SMP_Block()
- _Scheduler_SMP_Enqueue_scheduled_ordered()
- _Scheduler_SMP_Enqueue_scheduled_ordered()
+ schedulerprioritysmpimpl.h is a new file with prototypes for methods
which were formerly static in schedulerprioritysmp.c but now need to
be public to be shared with this scheduler.
NOTE:
_Scheduler_SMP_Get_lowest_ready() appears to have a path which would
allow it to return a NULL. Previously, _Scheduler_SMP_Enqueue_ordered()
would have asserted on it. If it cannot return a NULL,
_Scheduler_SMP_Get_lowest_ready() should have an assertions.
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Rename _Scheduler_Update() to _Scheduler_Update_priority(). Add
parameter for the new thread priority to avoid direct usage of
Thread_Control::current_priority in the scheduler operation.
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Replace _Scheduler_Allocate() with _Scheduler_Node_initialize(). Remove
the return status and thus the node initialization must be always
successful.
Rename _Scheduler_Free() to _Scheduler_Node_destroy().
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Extract code from _Scheduler_SMP_Enqueue_ordered() and move it to the
new function _Scheduler_SMP_Enqueue_scheduled_ordered() to avoid
untestable execution paths.
Add and use function _Scheduler_SMP_Unblock().
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The function to change a thread priority was too complex. Simplify it
with a new scheduler operation. This increases the average case
performance due to the simplified logic. The interrupt disabled
critical section is a bit prolonged since now the extract, update and
enqueue steps are executed atomically. This should however not impact
the worst-case interrupt latency since at least for the Deterministic
Priority Scheduler this sequence can be carried out with a wee bit of
instructions and no loops.
Add _Scheduler_Change_priority() to replace the sequence of
- _Thread_Set_transient(),
- _Scheduler_Extract(),
- _Scheduler_Enqueue(), and
- _Scheduler_Enqueue_first().
Delete STATES_TRANSIENT, _States_Is_transient() and
_Thread_Set_transient() since this state is now superfluous.
With this change it is possible to get rid of the
SCHEDULER_SMP_NODE_IN_THE_AIR state. This considerably simplifies the
implementation of the new SMP locking protocols.
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Use the basic Scheduler_Context for the general SMP scheduler operations
to avoid usage of structure offsets to get the specialized context
variants.
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Rename scheduler per-thread information into scheduler nodes using
Scheduler_Node as the base type. Use inheritance for specialized
schedulers.
Move the scheduler specific states from the thread control block into
the scheduler node structure.
Validate the SMP scheduler node state transitions in case RTEMS_DEBUG is
defined.
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Do not allocate the scheduler control structures from the workspace.
This is a preparation step for configuration of clustered/partitioned
schedulers on SMP.
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Scheduler operations must be free of a global scheduler context to
enable partitioned/clustered scheduling.
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