The effective use of processor cores and threads is a critically important element in capitalizing on the performance potential of a modern processor.
Makes sense. But what new technologies are available to make processors soar?
In this blog, I describe two of the features of IBM® POWER8™: multi-core and multi-threading technologies. Although these are not new technologies, they are constantly being stepped up.
In POWER8, which runs in AIX®, IBM i, and Linux environments:
- The POWER8 processor now has more cores
- POWER8 supports eight simultaneous multi-threading (SMT) hardware threads/core
Let’s describe the multi-core and mult-threading technologies briefly.
IBM® POWER7™ and IBM® POWER7+™ support eight cores/chip. POWER8 progresses to 12 cores/chip, each with its own 512 KB L2 and 8 MB L3 (embedded DRAM) cache, two memory controllers, PCIe Gen3 I/O controllers, and an interconnection system that connects all components within the chip. Having twelve cores empowers you to:
- Tune your IBM Power Systems™ for optimal performance
- Take advantage of the Power Systems features you most need
POWER7 and POWER7+ support four SMT hardware threads/core (or SMT4). POWER8 provides eight SMT hardware threads/core (or SMT8), so it can be configured to run in SMT8 mode, or in the previously-available SMT modes (SMT4, SMT2, or SMT1 (ST)). With multiple hardware threads per physical processor core, multiple streams of instructions can run simultaneously.
As an example, with multi-threaded POWER8 cores, each processor core can be instantiated with one, two, four, or eight logical CPUs within the operating system, so a 12-core server, with SMT8 mode, means that the operating system is running 96 logical CPUs.
SMT is primarily beneficial in commercial environments where the speed of an individual transaction is not as important as the total number of transactions performed. SMT is expected to increase the throughput of workloads with large or frequently changing working sets, such as database servers and web servers.
Multi-cores plus mult-threads
By configuring the processor cores to run in multi-threaded mode, your workloads can take advantage of the Power processor hardware and software features, including:
- The operating system can maximize the use of the hardware capabilities in the partition.
- The overall workload throughput is maximized by balancing the software threads across all of the cores and the SMT hardware threads in the partition.
Download the book, Performance Optimization and Tuning Techniques for IBM Processors, including IBM POWER8, free of charge at http://www.redbooks.ibm.com/redpieces/abstracts/sg248171.html.
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