STREAMS/UX for the HP 9000 Reference Manual

STREAMS/UX Multiprocessor Support

Running Modules and Drivers in Uniprocessor Emulation Mode

mode. Another example is STREAMS/UX pipes, which are MP scalable. If UP

emulation modules are pushed onto a pipe, the pipe runs under UP emulation.

• As described earlier in this section, all user bufcall callback functions are

executed in UP emulation mode. If an MP scalable module calls bufcall, the

callback routine runs under UP emulation. If the callback routine invokes a put

procedure, the put procedure also runs in UP emulation mode. For example, the

DLPI driver is MP scalable in 10.0 and calls bufcall. The bufcall callback

function runs under UP emulation.

Performance

Performance of UP emulation modules and drivers will likely worsen as

more processors are added to a system. If a large number of users will be

running your modules and drivers on MP systems, you should probably

modify the code to be MP scalable.

MP scalable modules that run over non-STREAMS/UX UP emulation

drivers will be forced to run in UP emulation mode. You can achieve better

performance by changing drivers to be MP scalable.

Guidelines for UP Emulation Modules and Drivers

• It is easier to develop STREAMS/UX based software which runs completely

under UP emulation or is completely MP scalable. Try to avoid mixing UP

emulation and MP scalable modules and drivers in the same stream or

multiplexor.

• It may be safe for UP emulation modules and drivers to call MP scalable

non-STREAMS software. The MP scalable software must be able to run while

the I/O semaphore is held. Note that if a put or service routine calls

non-STREAMS functions, these functions cannot acquire semaphores because

this might cause the put or service routine to block.

• Be careful with MP scalable non-STREAMS kernel code when calling UP

emulation STREAMS/UX modules. It is better if the non-STREAMS code

schedules a service routine instead of invoking a put procedure. Scheduling the

service routine will wake up the UP emulation scheduler daemon to run the

routine. The daemon acquires the I/O semaphore. If non-STREAMS code calls

put, putnext, or streams_put, STREAMS/UX will not acquire either the I/O

semaphore or the spl lock.

• Modules and drivers which can run MP scalable and run under UP emulation

must use queue or queue pair synchronization. An example of an MP scalable