STREAMS/UX for the HP 9000 Reference Manual

STREAMS/UX Multiprocessor Support

Writing MP Scalable Modules and Drivers

and sad drivers use global synchronization. Only one driver function in

ECHO-A, ECHO-B, DLPI-A and SAD-A can run at a time. However, one

of these drivers could run in parallel with a module conﬁgured for a

synchronization level other than global. All modules conﬁgured with global

synchronization can share data.

The STREAMS/UX synchronization levels also apply to open and close.

For example, if a module is conﬁgured for queue pair synchronization, none

of the put or service routines for the queue pair can run at the same time as

the queue pair's open or close. Also, open cannot run at the same time as

close. The least amount of protection that STREAMS/UX provides for

opens and closes is queue pair. Even if a module is conﬁgured with queue

synchronization, it will run as if it were conﬁgured with queue pair

synchronization during opens and closes.

STREAMS/UX provides additional protection for opens and closes.

STREAMS/UX executes only one open or close across all streams at a time.

For example in Figure 1, if STREAMS/UX is executing the ECHO-A echo

driver's open routine, the DLPI-A dlpi open cannot run nor can any other

module's or driver's open or close. An exception to this occurs if an open or

close sleeps. When this happens, other opens and closes can occur. An open

or close function that sleeps may need to use a spinlock together with the

get_sleep_lock, SV_WAIT or SV_WAIT_SIG utilities to prevent missing

wakeups. These utilities are described in the “HP-UX Modiﬁcations to

STREAMS/UX Utilities” section in Chapter 3. Also, SV_WAIT and

SV_WAIT_SIG are discussed in the SVR4.2 Driver manual.

STREAMS does not synchronize the running of timeout and bufcall

callback functions with modules and drivers. This chapter lists some

restrictions on what these callback functions can do.

Suggestions for Designing MP Scalable Modules and Drivers

This section contains recommendations for designing MP scalable modules

and drivers:

• Modules and drivers that run over UP emulation hardware drivers must run under

UP emulation. Before changing STREAMS/UX modules and drivers to be MP

scalable, modify hardware drivers to be MP scalable.

• You can improve the performance of modules and drivers by using the elsewhere

synchronization level. Configure all modules and drivers in a subsystem to be in