Flag D

Flag D_MP

You specify D_MP in pfxdevflag to tell lboot that your driver is designed to operate in a multiprocessor system. The top half of the driver is designed to cope with multiple concurrent entries in multiple CPUs. The top and bottom halves synchronize through the use of semaphores or locks and do not rely on interrupt masking for critical sections. These issues are discussed further under "Planning for Multiprocessor Use".

When D_MP is not present in pfxdevflag, IRIX ensures that the driver code, including the upper-half entry points and the interrupt handler, executes only on CPU 0 of a multiprocessor. This ensures behavior similar to a uniprocessor, but can cause a performance bottleneck when either the device or CPU 0 is heavily used.

Note: This flag is only tested when loading a character driver or STREAMS driver. There is no special handling for block drivers and network drivers in multiprocessors. Block and network drivers must be multiprocessor-aware.