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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.
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Planning, Installing, and Managing the IBM System x3950 M2
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