| Commit message (Collapse) | Author | Age | Files | Lines |
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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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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.
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