Understanding Scheduling, Thread Context, and IRQL -- 18

Scheduling, Thread Context, and IRQL

ThángTư11,2012

Abstract

This paper presents information about how thread scheduling, thread context, and a processor’s current interrupt request level (IRQL) affect the operation of kernel - mode drivers for the Microsoftđ Windowsđ family of operating systems. It is intended to provide driver writers with a greater understanding of the environment in which their code runs.

A companion paper, “Locks, Deadlocks, and Synchronization” at http://www. microsoft. com/whdc/hwdev/driver/LOCKS. mspx, builds on these fundamental concepts to address synchronization issues in drivers.

Contents

Introduction              2

Thread Scheduling              2

Thread Context and Driver Routines              3

Driver Threads              4

Interrupt Request Levels              5

Processor - specific and Thread - specificIRQLs              6

IRQL PASSIVE_ LEVEL              7

IRQL PASSIVE_ LEVEL in a critical region              7

IRQL APC_ LEVEL              7

IRQL DISPATCH_ LEVEL              8

IRQL DIRQL              9

IRQL HIGH_ LEVEL              10

Guidelines for Running at IRQL DISPATCH_ LEVEL or Higher              10

Changing the IRQL at which Driver Code Runs              11

Standard Driver Routines, IRQL, and Thread Context              12

Interrupting a Thread: Examples              14

Single - Processor Example              15

Multiprocessor Example              16

Testing for IRQL Problems              17

Techniques for Finding the Current IRQL              17

PAGED_ CODE Macro              17

Driver Verifier Options              17

Best Practices for Drivers              18

Call to Action and Resources              18

Disclaimer

This is a preliminary document and may be changed substantially prior to final commercial release of the software described herein.

The information contained in this document represents the current view of Microsoft Corporation on the issues discussed as of the date of publication. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information presented after the date of publication.

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