Multithreading device drivers

A multithreaded device driver can run its task-time code and/or its interrupt handler routine on any processor in a multiprocessor configuration. The coding practices necessary to multithread a driver fall in two categories:

• code to register the driver as multithreaded during system or driver initialization.

• code to protect critical code segments from processes running on other CPUs.

Single-threaded drivers can run on multiprocessing configurations, but they are restricted to the base processor and do not benefit from the performance advantages of the multiprocessing architecture. In fact, having single-threaded drivers running on a multiprocessing system may seriously degrade system performance. Multithreaded drivers, on the other hand, can run on uniprocessor configurations without modification. Theoretically, a multithreaded driver may be a bit slower than a single-threaded driver on a uniprocessor system, but the difference is seldom noticeable.

SCO recommends that all new device drivers be written to be multithreaded unless there is a compelling reason not to. This chapter provides information to help in this task:

• an overview of the design of SCO multiprocessor systems

• instructions for registering a driver as multithreaded

• instructions for protecting critical code sections

• specific notes about multithreading block drivers

Other information about multithreading drivers is contained elsewhere in the HDK documentation set:

• information about multithreading TTY drivers

• information about multithreading SCSI host adapter drivers

• information about multithreading SCSI peripheral drivers