Hello,
with the reworked thread priority management we have now all information
available to feed the schedulers and implement the last step of the OMIP
locking protocol.
https://devel.rtems.org/ticket/2556
The remaining work is mostly SMP only. We have two major locking domains
for threads, one is the thread wait domain (thread queues) and the other
is the thread state (scheduler related) domain. The thread wait domain
needs to pass the thread priority information to the thread state
domain. This will be done via a dedicated low-level SMP lock
(Thread_Control::Scheduler::Lock) and disabled thread dispatching. Each
thread may use multiple scheduler instances (clustered scheduling) due
to the locking protocols (MrsP and OMIP).
The first approach to implement MrsP had several severe design flaws. I
will replace it and use a thread queue instead. So, the Resource Handler
will be removed entirely
(https://git.rtems.org/rtems/tree/cpukit/score/include/rtems/score/resource.h).
The first scheduler helping protocol used a return value to indicate
threads in need for help. There are three problems with this approach.
Firstly, you can return at most one thread, but multiple threads in need
for help may be produced by one operation, e.g. due to affinity
constraints. Secondly, the thread the initiated the operation must carry
out the ask for help operation. This is bad in terms of scheduler
instance isolation, e.g. high priority thread H in instance A sends a
message to worker thread in instance B, H must execute scheduler code of
instance B. Thirdly, it complicates the SMP low-level locking. I will
change this to use an SMP message processed via an
inter-processor-interrupt.
Once the OMIP implementation is done, the SMP support for RTEMS is
feature complete from my point of view. There are still some interesting
things to do, but the ground work is done and I think we have a
state-of-the-art feature set in real-time SMP systems area.
--
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
PGP : Public key available on request.
Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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