Windows® 2000 Device Driver Book: A Guide for Programmers, Second Edition, The

Deferred Procedure Calls (DPCs)

While a piece of kernel-mode code is running at an elevated IRQL, nothing executes (on the same CPU) at that or any lower IRQL. Of course, if too much code executes at too high an IRQL, overall system performance will degrade. Time-critical event handling could be deferred and cause more disastrous results.

To avoid these problems, kernel-mode code must be designed to execute as much code as possible at the lowest possible IRQL. One important part of this strategy is the Deferred Procedure Call (DPC).

Operation of a DPC

The DPC architecture allows a task to be triggered, but not executed, from a high-level IRQL. This deferral of execution is critical when servicing hardware interrupts in a driver because there ...