STREAMS/UX for the HP 9000 Reference Manual

STREAMS/UX Multiprocessor Support

Running Modules and Drivers in Uniprocessor Emulation Mode

Running Modules and Drivers in Uniprocessor

Emulation Mode

STREAMS/UX supports uniprocessor emulation for modules and drivers.

Modules and drivers which run on uniprocessor systems can run on

multiprocessor systems under UP emulation without code changes. This

section presents an overview of UP emulation, describes how to conﬁgure

modules and drivers for UP emulation, describes what happens when a

stream contains both UP emulation and MP scalable modules, and describes

how UP emulation affects performance. Lastly, this section contains some

UP emulation programming guidelines.

How STREAMS/UX Executes UP Emulation Modules and Drivers

This section describes how STREAMS/UX supports UP emulation. HP-UX

provides UP emulation for non-STREAMS device drivers which were

developed for uniprocessor systems.

HP-UX uses a semaphore called the I/O semaphore and a spinlock known as

the spl lock to implement UP emulation. HP-UX uses the I/O semaphore to

serialize driver system calls. HP-UX acquires the I/O semaphore before

calling the driver to process a system call. HP-UX uses the spl lock to

prevent a driver interrupt on one processor from running in parallel with a

driver system call on another processor. When a driver calls spln to raise the

spl level, HP-UX acquires the spl lock. When an interrupt occurs for a UP

emulation driver, HP-UX acquires the spl lock before calling the driver's

interrupt handler.

STREAMS/UX extends UP emulation for STREAMS/UX modules and

drivers. A stream can be entered in two ways. One way is through a system

call. Either the I/O system or STREAMS/UX acquires the I/O semaphore

before executing a system call for a UP emulation stream. Also, a stream

can be entered from non-STREAMS software in the kernel. For example, an

interrupt handler can call putq, putnext,put, or streams_put to enter a stream.

If code on the interrupt control stack (ICS) calls putq for a UP emulation

stream, the STREAMS/UX UP emulation scheduler runs the service routine.

This scheduler acquires the I/O semaphore. If an interrupt occurs for a UP