On 05/29/2014 09:28 PM, Joel Sherrill wrote:
Hi
The priority affinity algorithm appears to be behaving as
we expect from a decision making standpoint. However,
Jennifer and I think that when a scheduled thread must
be migrated to another core, we have a case for a new
state in the Thread Life Cycle.
I hope we can avoid this. Which problem do you want to address with
this new state?
I am thinking that the thread needs to have a blocking state
set, have its context saved and be taken out of the scheduled
set. Then a life cycle state change handler van run as an
extension to unblock it so it can be potentially scheduled to
execute on another processor.
The scheduler is not responsible for the thread context. This is
_Thread_Dispatch(). A post-switch handler can only do actions for the
executing thread. It would be extremely difficult to perform actions on
behalf of another thread. We have to keep also fine grained locking
into account. The _Thread_Dispatch() function is on the critical path
for average and worst-case performance, so we should keep it as simple
as possible.
As I wrote already in another thread you can use something like this to
allocate an exact processor for a thread:
static inline void _Scheduler_SMP_Allocate_processor_exact(
Scheduler_SMP_Context *self,
Thread_Control *scheduled,
Thread_Control *victim
)
{
Scheduler_SMP_Node *scheduled_node = _Scheduler_SMP_Node_get(
scheduled );
Per_CPU_Control *cpu_of_scheduled = _Thread_Get_CPU( scheduled );
Per_CPU_Control *cpu_of_victim = _Thread_Get_CPU( victim );
Per_CPU_Control *cpu_self = _Per_CPU_Get();
_Scheduler_SMP_Node_change_state(
scheduled_node,
SCHEDULER_SMP_NODE_SCHEDULED
);
_Thread_Set_CPU( scheduled, cpu_of_victim );
_Scheduler_SMP_Update_heir( cpu_self, cpu_of_victim, scheduled );
}
You can even use this function to do things like this:
_Scheduler_SMP_Allocate_processor_exact(self, executing, other);
_Scheduler_SMP_Allocate_processor_exact(self, other, executing);
This works because the is executing indicator moved to the thread
context and is maintained at the lowest context switch level. For
proper migration the scheduler must ensure that,
1. an heir thread other than the migrating thread exists on the source
processor, and
2. the migrating thread is the heir thread on the destination processor.
--
Sebastian Huber, embedded brains GmbH
Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone : +49 89 189 47 41-16
Fax : +49 89 189 47 41-09
E-Mail : sebastian.hu...@embedded-brains.de
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Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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