Chapter 46. Pentium^® 4 Priority Agent Arbitration

The Previous Chapter

This chapter provided a detailed description of how the processors arbitrate for ownership of the FSB. It included:

• The Request Phase.

• Logical versus Physical Processors.

• No External Arbiter Required.

• The Rotating ID.

• The Busy/Idle Indicator.

• Requesting Ownership.

• Definition of an Arbitration Event.

This Chapter

This chapter provides a detailed description of how priority agents arbitrate for ownership of the FSB. It includes:

• Priority Agent Arbitration—Despotism.

• Example Priority Agents.

• Priority Agent Beats Symmetric Agents, Unless...

• Using Simple Approach, Priority Agent Suffers Penalty.

• Smarter Priority Agent Gets Ownership Faster.

• Ownership Attained in 1 BCLK.

• Ownership Attained in 2 BCLKs.

• Be Fair to the Common People.

• Priority Agent Parking.

The Next Chapter

This chapter describes the FSB locking mechanism, the reason for its existence, and the instructions that invoke it. It includes:

• The Shared Resource Concept.

• Testing the Availability of and Gaining Ownership of Shared Resources.

• A Race Condition Can Present a Problem.

• Guaranteeing the Atomicity of a Read/Modify/Write.

• Locking a Cache Line.