PCI Prefetch – The BIOS Optimization Guide

PCI Prefetch - The BIOS Optimization Guide

PCI Prefetch

Common Options : Enabled, Disabled

 

Quick Review

The PCI Prefetch feature controls the PCI controller’s prefetch capability.

When enabled, the PCI controller will prefetch data whenever the PCI device reads from the system memory. This speeds up PCI reads as it allows contiguous memory reads by the PCI device to proceed with minimal delay.

Therefore, it is recommended that you enable this feature for better PCI read performance.

 

Details

The PCI Prefetch feature controls the PCI controller’s prefetch capability.

When enabled, the system controller will prefetch eight quadwords (one cache line) of data whenever a PCI device reads from the system memory.

Therefore, it is recommended that you enable this feature for better PCI read performance. Please note that PCI writes to the system memory do not benefit from this feature.

Here’s how it works.

Whenever the PCI controller reads PCI-requested data from the system memory, it also reads the subsequent cache line of data. This is done on the assumption that the PCI device will request for the subsequent cache line.

When the PCI device actually initiates a read command for that cache line, the system controller can immediately send it to the PCI device.

This speeds up PCI reads as the PCI device won’t need to wait for the system controller to read from the system memory. As such, PCI Prefetch allows contiguous memory reads by the PCI device to proceed with minimal delay.

 

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