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Process, Interrupt Affinity on Intel® Xeon® Processor E5 Servers

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Process, Interrupt Affinity on Intel® Xeon® Processor E5 Servers

The designs of the new Intel® Xeon® E5 processor servers have introduced some complexities that, if not accommodated in the application design, may not produce as large a performance gain as possible. Creating core affinity is critical in a Direct Data IO/NUMA environment. Whenever possible, processes that are identified as performance-critical should have affinity with the local socket connection, rather than remote socket connections. To that end, the most foolproof method for identifying the local and remote socket might be to refer to the block diagram of the server platform. This might not always be as easy as it is with the Intel®Software Development Vehicle (SDV) code name: Rose City, where all the PCIE slots were branched off of a single socket/CPU1.

The example in the picture below shows the I/O riser module from a Dell R720* series server, an Intel Xeon E5 processor platform where the riser clearly identifies slot affinity to a given CPU or socket.

Another way to determine socket correlation would be to use APICID reference under/proc/cpuinfo, or possibly the CPU-Z detection engine for Windows*. (Assuming the APIC tables are implemented as defined in ACPI 5.0 specification and the operating system is able to read and parse the information for application consumption.) Once the local socket is identified and a determination is made about how to distribute the processes. (Keep in mind that simultaneous multi-threading (SMT) is especially effective when each thread is set to perform different types of operations and perform those operations with under-used CPU cycles.) Then, use the Thread Affinity Interface to assign the processes to the cores as needed.

Read the full Process, Interrupt Affinity on Intel® Xeon® Processor E5 Servers application note: http://www.intel.com/content/www/us/en/processors/xeon/xeon-e5-ddio-appl-notes.html