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.
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.
Fix context switch on SMP for ARM, PowerPC and SPARC.
Atomically test and set the is executing indicator of the heir context
to ensure that at most one processor uses the heir context. Break the
busy wait loop also due to heir updates.
Rename bsp_mm_config_table to arm_cp15_start_mmu_config_table and
rename bsp_mm_config_table_size to arm_cp15_start_mmu_config_table_size
to be in line with the other names in <bsp/arm-cp15-start.h>.
.. according to the maximum number of termios ports which is
8. Since LEON3 uses PnP to find how many UARTs there are
present we must make sure worst case work.
The current maximum of 4 free nodes caused for example the
GR712RC with its 6 UARTs to fail during devfs02 test.
On SMP rtems_interrupt_lock_context must be used. Most tests fail with a
NULL pointer exception when exiting, except on NGMP where main memory is
at 0x00000000.
The _CPU_Context_Restart_self() implementations usually assume that self
context is executing.
FIXME: We have a race condition in _Thread_Start_multitasking() in case
another thread already performed scheduler operations and moved the heir
thread to another processor. The time frame for this is likely too
small to be practically relevant.
Close the thread object in _Thread_Make_zombie() so that all blocking
operations that use _Thread_Get() in the corresponding release directive
can find a terminating thread and can complete the operation.
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.
Remove the scheduler parameter from most high level scheduler operations
like
- _Scheduler_Block(),
- _Scheduler_Unblock(),
- _Scheduler_Change_priority(),
- _Scheduler_Update_priority(),
- _Scheduler_Release_job(), and
- _Scheduler_Yield().
This simplifies the scheduler operations usage.
Suppose we have two tasks A and B and two processors. Task A is about
to delete task B. Now task B calls rtems_task_wake_after(1) on the
other processor. Task B will block on the Giant lock. Task A
progresses with the task B deletion until it has to wait for
termination. Now task B obtains the Giant lock, sets its state to
STATES_DELAYING, initializes its watchdog timer and waits. Eventually
_Thread_Delay_ended() is called, but now _Thread_Get() returned NULL
since the thread is already marked as deleted. Thus task B remained
forever in the STATES_DELAYING state.
Instead of passing the thread identifier use the thread control block
directly via the watchdog user argument. This makes
_Thread_Delay_ended() also a bit more efficient.
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.
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.
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.
When trying to compile RTEMS for the Stellaris LM3S6965 board, I had an
issue of pppd.exe's .rodata section being too big to fit in the board's
memory image (region 'ROM_INT' overflowed).
Joel Sherrill
Sebastian Huber
Daniel Hellstrom
Martin Galvan