IBM 88743BU User Manual - Page 126
Processor Hardware Prefetcher, Processor Execute Disable Bit
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Note: Intel recommends testing both enabled and disabled settings and then setting the adjacent sector prefetch accordingly after performance evaluation. For instance, only one 64-byte line from the 128-byte sector will be prefetched with this setting disabled. This setting can affect performance, depending on the application running on the server and memory bandwidth utilization. Typically, it affects certain benchmarks by a few percent, although in most real applications it will be negligible. This control is provided for benchmark users who want to fine-tune configurations and settings. Processor Hardware Prefetcher When this setting is enabled, the processors are able to prefetch extra cache lines for every memory request. Recent tests in the performance lab have shown that you can get the best performance for most commercial application types if you disable this feature. The performance gain can be as much as 20% depending on the application. For high-performance computing (HPC) applications, we recommend that you enable the Processor Hardware Prefetch option; for database workloads, we recommend you disable the option. Note: Intel recommends that the Processor Hardware Prefetcher be enabled for server workloads similar to the Streams Benchmark, but that the actual setting should be determined by performance testing in your intended workload environment. Processor Execute Disable Bit Processor Execute Disable Bit (EDB or XD) is a function of new Intel processors which lets you prevent the execution of data that is in memory as though it was code. When this setting is enabled (the default), viruses or other malicious code are prevented from gaining unauthorized access to applications by exploiting buffer overruns in those applications. If this option is enabled, and the operating system has marked the memory segment as containing data, then the processor will not execute any code in the segment. This parameter can be disabled in the BIOS, if the applications to run on the server have problems with Execution Prevention. For added protection, you might want to enable it, but you should first test your applications to ensure they can continue to run as expected before you enable the option in a production environment. 108 Planning, Installing, and Managing the IBM System x3950 M2