Clustered/partitioned scheduling helps to control the worst-case
latencies in the system. The goal is to reduce the amount of shared
state in the system and thus prevention of lock contention. Modern
multi-processor systems tend to have several layers of data and
instruction caches. With clustered/partitioned scheduling it is
possible to honour the cache topology of a system and thus avoid
expensive cache synchronization traffic.
We have clustered scheduling in case the set of processors of a system
is partitioned into non-empty pairwise-disjoint subsets. These subsets
are called clusters. Clusters with a cardinality of one are partitions.
Each cluster is owned by exactly one scheduler instance.
The thread control block contains fields that point to application
configuration dependent memory areas, like the scheduler information,
the API control blocks, the user extension context table, the RTEMS
notepads and the Newlib re-entrancy support. Account for these areas in
the configuration and avoid extra workspace allocations for these areas.
This helps also to avoid heap fragementation and reduces the per thread
memory due to a reduced heap allocation overhead.
Do not allocate the scheduler control structures from the workspace.
This is a preparation step for configuration of clustered/partitioned
schedulers on SMP.
This simplifies the RTEMS initialization and helps to avoid a memory
overhead. The workspace demands of the IO manager were not included in
the <rtems/confdefs.h> workspace size estimate. This is also fixed as a
side-effect.
Update documentation and move "Specifying Application Defined Device
Driver Table" to the section end. This sub-section is not that
important for the user. Mentioning this at the beginning may lead to
confusion.
Per task variables are inherently unsafe in SMP systems. This
patch disables them from the build and adds warnings in the
appropriate documentation and configuration sections.
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.
This partially reverts commit 1215fd4d94.
In order to support profiling of SMP locks and provide a future
compatible SMP locks API it is necessary to add an SMP lock destroy
function. Since the commit above adds an SMP lock to each chain control
we would have to add a rtems_chain_destroy() function as well. This
complicates the chain usage dramatically. Thus revert the patch above.
A global SMP lock for all chains is used to implement the protected
chain operations.
Advantages:
* The SAPI chain API is now identical on SMP and non-SMP
configurations.
* The size of the chain control is reduced and is then equal to the
Score chains.
* The protected chain operations work correctly on SMP.
Disadvantage:
* Applications using many different chains and the protected operations
may notice lock contention.
The chain control size drop is a huge benefit (SAPI chain controls are
66% larger than the Score chain controls). The only disadvantage is not
really a problem since these applications can use specific interrupt
locks and unprotected chain operations to avoid this issue.
Formerly POSIX keys were only enabled when POSIX threads
were enabled. Because they are a truly safe alternative
to per-task variables in an SMP system, they are being
enabled in all configurations.
Add a CPU counter interface to allow access to a free-running counter.
It is useful to measure short time intervals. This can be used for
example to enable profiling of critical low-level functions.
Add two busy wait functions rtems_counter_delay_ticks() and
rtems_counter_delay_nanoseconds() implemented via the CPU counter.
Rename rtems_internal_error_description() to
rtems_internal_error_text(). Rename rtems_fatal_source_description() to
rtems_fatal_source_text(). Rename rtems_status_code_description() to
rtems_status_text(). Remove previous implementation of
rtems_status_text().
Add ISR lock to chain control for proper SMP protection. Replace
rtems_chain_extract() with rtems_chain_explicit_extract() and
rtems_chain_insert() with rtems_chain_explicit_insert() on SMP
configurations. Use rtems_chain_explicit_extract() and
rtems_chain_explicit_insert() to provide SMP support.
Change pthread_once from using disabled pre-emption to using a
pthread mutex making it SMP safe. GCC using a posix threading
model uses pthread_once.
The pthread mutex requires at least 1 mutex is configured so
confdefs.h has been updated to account for the internal
mutex.
This patch enables unlimited model in POSIX key manger and have a decent
runtime on POSIX key searching, adding and deleting operations. Memory
overhead is lower than current implementation when the size of key and key
value becomes big.
Move implementation specific parts of object.h and object.inl into new
header file objectimpl.h. The object.h contains now only the
application visible API.
Move implementation specific parts of extension.h and extension.inl into
new header file extensionimpl.h. The extension.h contains now only the
application visible API.
Move implementation specific parts of chain.h and chain.inl into new
header file chainimpl.h. The chain.h contains now only the application
visible API.
Move implementation specific parts of message.h and message.inl into new
header file messageimpl.h. The message.h contains now only the
application visible API.
A common use case for disabled preemption was to ensure mutual exclusion
on single-processor configurations. On SMP this does not work.
To abandon non-preemptible tasks simplifies the scheduler.
Add a configuration field which indicates if the SMP mode of operation
is enabled. This can be used to disable features unsupported on SMP,
e.g task variables.
