Tag Archives: Prefetch

PCI Prefetch - The BIOS Optimization Guide

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.

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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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CPU Hardware Prefetch – The BIOS Optimization Guide

CPU Hardware Prefetch

Common Options : Enabled, Disabled

 

Quick Review

The processor has a hardware prefetcher that automatically analyzes its requirements and prefetches data and instructions from the memory into the Level 2 cache that are likely to be required in the near future. This reduces the latency associated with memory reads.

When enabled, the processor’s hardware prefetcher will be enabled and allowed to automatically prefetch data and code for the processor.

When disabled, the processor’s hardware prefetcher will be disabled.

If you are using a C1 stepping (or older) of the Intel Pentium 4 or Intel Pentium 4 Xeon processor, it is recommended that you enable this BIOS feature so that the hardware prefetcher is enabled for maximum performance.

But if you are using an older version of the Intel Pentium 4 or Intel Pentium 4 Xeon processor, then you should disable the CPU Hardware Prefetch BIOS feature to circumvent the O37 bug which causes data corruption when the hardware prefetcher is operational.

 

Details

CPU Hardware Prefetch is a BIOS feature specific to processors based on the Intel NetBurst microarchitecture (e.g. Intel Pentium 4 and Intel Pentium 4 Xeon).

These processors have a hardware prefetcher that automatically analyzes the processor’s requirements and prefetches data and instructions from the memory into the Level 2 cache that are likely to be required in the near future. This reduces the latency associated with memory reads.

When it works, the hardware prefetcher does a great job of keeping the processor loaded with code and data. However, it doesn’t always work right.

Prior to the C1 stepping of the Intel Pentium 4 and Intel Pentium 4 Xeon, these processors shipped with a bug that causes data corruption when the hardware prefetcher was enabled. According to Intel, Errata O37 causes the processor to “use stale data from the cache while the Hardware Prefetcher is enabled“.

Unfortunately, the only solution for the affected processors is to disable the hardware prefetcher. This is where the CPU Hardware Prefetch BIOS feature comes in.

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When enabled, the processor’s hardware prefetcher will be enabled and allowed to automatically prefetch data and code for the processor.

When disabled, the processor’s hardware prefetcher will be disabled.

If you are using a C1 stepping (or older) of the Intel Pentium 4 or Intel Pentium 4 Xeon processor, it is recommended that you enable this BIOS feature so that the hardware prefetcher is enabled for maximum performance.

But if you are using an older version of the Intel Pentium 4 or Intel Pentium 4 Xeon processor, then you should disable this BIOS feature to circumvent the O37 bug which causes data corruption when the hardware prefetcher is operational.

 

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