STREAMS/UX for the HP 9000 Reference Manual

STREAMS/UX Multiprocessor Support

Writing MP Scalable Modules and Drivers

the same group. They can all share data. However, STREAMS/UX will not

synchronize bufcall and timeout callback functions or any non-STREAMS/UX

code with the modules or drivers. You may be able to use the streams_put utility

described in Chapter 3. In general, UP emulation provides more protection for

bufcall, timeout, and non-STREAMS functions.

• To change modules and drivers to be MP scalable, analyze how the code shares

data structures. Determine which structures are shared and which module and

driver entry points read and write to the structures. Using this information, choose

synchronization levels for modules and drivers that correctly serialize access to

shared data.

• If all modules and drivers of a product share the same structure, consider

changing the module and driver data structures and algorithms to allow for more

parallelism. Alternatively, consider using spinlocks to protect shared structures

that are accessed infrequently or for short amounts of time. Using spinlocks is a

good way to protect structures which are not accessed on the main read and write

paths. You can either use the native HP-UX spinlock primitives or the SVR4 MP

LOCK, TRYLOCK, UNLOCK, LOCK_ALLOC and LOCK_DEALLOC utilities.

The SVR4 MP utilities are discussed under “HP-UX Modifications to

STREAMS/UX Utilities” in Chapter 3 and in the SVR4.2 Driver manual.

• Use service routines only for flow control, recovering from resource shortages or

executing interrupt completions in a process context. Service routines degrade

performance.

• Be careful when writing timeout and bufcall callback functions, as well as

non-STREAMS code that calls STREAMS/UX utilities or shares data with

modules and drivers. See the “Guidelines for MP Scalable Modules and Drivers”

section.

Configuring MP Scalable Modules and Drivers

This section describes how to conﬁgure MP scalable modules and drivers.

MP Scalable Module and Driver Configuration

If you want a module or driver to be MP scalable, you must specify

additional conﬁguration parameters. You need to:

• Add a flag indicating that the module or driver is MP scalable

• Add a keyword which specifies the synchronization level the module or driver

uses

• Add a sync name if the module or driver requires elsewhere synchronization