KeRaiseIrqlToDpcLevel

KeRaiseIrqlToDpcLevel is a kernel-mode routine in the Windows operating system that raises the current IRQL (Interrupt Request Level) to the DISPATCH_LEVEL, the IRQL at which DPCs (Deferred Procedure Calls) run. The function records the caller’s previous IRQL in an out parameter so that it can be restored later, typically with KeLowerIrql. By elevating to DPC level, the code prevents normal thread preemption and APC delivery while still allowing DPCs to execute, enabling short, non-blocking critical sections that must not be interrupted by thread scheduling.

Usage and behavior: The routine is used in low-level driver code that needs to protect a small, time-sensitive region from preemption by lower-priority threads. It is common to pair the call with a corresponding KeLowerIrql to restore the prior IRQL when the protected work is complete. The OldIrql value is supplied by the caller and represents the IRQL prior to the elevation.

Constraints and considerations: Raising IRQL to DPC level disables certain kernel activities and can impact system responsiveness if held for long periods. While at DISPATCH_LEVEL, code must avoid operations that may page memory, call functions that require pageable resources, or acquire resources that can cause the thread to block. Developers should minimize the duration of the IRQL elevation and be careful to avoid deadlocks or priority inversions. Misuse can lead to system instability, driver crashes, or deadlocks.

Related concepts: KeLowerIrql reverts the IRQL to the previous level. Other related routines include KeRaiseIrqlToSynchLevel for synchronization purposes and various spin-lock APIs that also elevate IRQL during acquisition. The function is part of the Windows Driver Kit and is documented for kernel-mode driver development.

See also: KeLowerIrql, KeRaiseIrqlToSynchLevel, spin-lock APIs, DPCs, IRQL concept.