STREAMS/UX for the HP 9000 Reference Manual

STREAMS/UX Multiprocessor Support

MP Synchronization Levels on a Uniprocessor

This section describes how modules and drivers can use MP synchronization

levels on a uniprocessor system to protect their private data structures

against interrupts. Please read “Writing MP Scalable Modules and Drivers”

in this chapter and “STREAMS/UX Uniprocessor Synchronization” in

Chapter 3 before reading this section.

In addition to the techniques described under “Driver and Module

Synchronization” in Chapter 3, modules and drivers can use MP

synchronization levels to protect their private structures against interrupts.

By default STREAMS/UX conﬁgures modules and drivers to use queue pair

synchronization. This is why modules and drivers do not need to raise the

spl level to protect their data if software running on the ICS sends a message

to a stream. Suppose an interrupt occurs while one of a queue pair's entry

points is running. STREAMS/UX will re-schedule sending the message to

the stream to after the entry point ﬁnishes executing. You can conﬁgure

uniprocessor modules and drivers to use synchronization levels other than

queue pair synchronization if they need more protection.

For example, you could conﬁgure a module to use module synchronization

if multiple instances of the module share the same data structure, and if the

module updates the structure when it is running on the ICS. If you conﬁgure

the module to use module synchronization, STREAMS/UX will wait until

no instances of the module are running before sending it a message.

Alternatively, you could change the module to raise the spl level while

accessing the shared structure.

You conﬁgure synchronization levels for modules and drivers that run on a

uniprocessor system in the same way as for MP scalable modules and

drivers. You must specify the synchronization level the module or driver

uses, and if the module or driver requires elsewhere synchronization, you

must specify a sync name. The sync name indicates which modules and

drivers belong to a group. Pick a sync name with 8 or fewer characters, and

conﬁgure the name for each member of the group. You conﬁgure the

synchronization level and the sync name in either the master ﬁle

$STREAMS_DVR_SYNC table or in an install function streams_info_t

structure.