Bound multiprocessing (BMP)

Bound multiprocessing provides the scheduling control of an asymmetric multiprocessing model, while preserving the hardware abstraction and management of symmetric multiprocessing.

BMP is similar to SMP, but you can specify which processors a thread can run on. You can use both SMP and BMP on the same system, allowing some threads to migrate from one processor to another, while other threads are restricted to one or more processors.

As with SMP, a single copy of the OS maintains an overall view of all system resources, allowing them to be dynamically allocated and shared among applications. But, during application initialization, a setting determined by the system designer forces all of an application's threads to execute only on a specified CPU.

Compared to full, floating SMP operation, this approach offers several advantages:

With BMP, an application locked to one CPU can't use other CPUs, even if they're idle. However, the QNX Neutrino RTOS lets you dynamically change the designated CPU, without having to checkpoint, and then stop and restart the application.

QNX Neutrino supports the concept of hard processor affinity through a runmask. Each bit that's set in the runmask represents a processor that a thread can run on. By default, a thread's runmask is set to all ones, allowing it to run on any processor. A value of 0x01 would allow a thread to execute only on the first processor.

By default, a process's or thread's children don't inherit the runmask; there's a separate inherit mask.

By careful use of these masks, a systems designer can further optimize the runtime performance of a system (e.g., by relegating nonrealtime processes to a specific processor). In general, however, this shouldn't be necessary, because our realtime scheduler will always preempt a lower-priority thread immediately when a higher-priority thread becomes ready. Processor locking will likely affect only the efficiency of the cache, since threads can be prevented from migrating.

You can specify the runmask for a new thread or process by:

You can change the runmask for an existing thread or process by:

For more information, see the Multicore Processing chapter of the QNX Neutrino Programmer's Guide.