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CPU Threading Efficiency: The Processor Consumed Value

CPU Threading Efficiency

This is the fifth installment in an ongoing series on improving AIX performance by emphasizing CPU threading efficiency. Read part 1, part 2, part 3 and part 4.

Decades ago, at the beginning of IT on UNIX, there was a universally expected shortfall of CPU cycles for enterprise workload processing. Back then, there was only a single CPU. Today of course, we have a vastly different landscape. Now we're working with multi-CPU architectures―make that high-concurrency, large-scale, multi-threading, multi-CPU shared-cache/shared-memory architectures. Obviously this is an exponential advancement of computing technology beyond one CPU and a range of mbRAM.

It should be noted though that UNIX (including AIX) has held close to a single-CPU perspective throughout. Despite the reality of some-to-many CPUs (and GBs-to-TBs of memory) in the hardware architecture, the operating system often represents many CPUs as a single "super CPU" and non-uniform memory architectures (NUMA) as a single simple chunk of memory. This explains why our monitoring perspectives are progressively less representative of how a workload actually manifests on a computing platform: Even as computing technology advances through generations, the operating system continues to present somewhat the same familiar view.

This delta between what the OS reports versus the reality on the hardware is further exacerbated by virtualization, consolidation and concurrency. By concurrency, I mean the system events of more and faster CPU, cache, memory, PCI lanes, etc., that are executing everything―i.e. the Power hypervisor and all LPAR kernel/user workloads―at the same time. So much more happens in the same clock cycle, yet we've not been adapting our awareness to this vastly greater scale of concurrent events.

In short―and as I've stated throughout this series―when it comes to capacity planning, our familiar traditions remain generally adequate. To conduct tactical monitoring though, we must also consider the complexities of virtualization, consolidation and concurrency alongside the activities of multiple CPUcores.

Tactical Details of the cpu:pc Value

In this article, you will learn the meaning of the processor consumed (cpu:pc) value.

As previously explained, the AIX:vmstat -IWwt 1 syntax uses a 1-second sampling interval. Our subject is the set of values that comprise the cpu:pc column, located at the far right of figure 1. The cpu:pc value is properly a main focus of all capacity monitoring utilities, but as always, I aim to add perspectives not otherwise considered when monitoring this value.

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