Chapter 3. Virtualization 101 Virtual processors do not introduce any additional abstraction level. They are only adispatch entity. On a physical processor, virtual processors run at the same speed as thephysical processor. Each partition’s profile defines CPU entitlement, which determines how much processingpower any given partition should receive. The total sum of CPU entitlement of all partitionscannot exceed the number of available physical processors in the pool. The number of virtual processors can be changed dynamically through a dynamic LPARoperation.Processor modeWhen you create a logical partition, you can assign entire processors for dedicated use, oryou can assign partial processor units from a shared processor pool. This setting defines theprocessing mode of the logical partition.Figure 3-4 shows a diagram of the concepts discussed in the remaining sections.Figure 3-4 Concepts on dedicated and shared processor modesDedicated modeIn dedicated mode, physical processors are assigned as a whole to partitions. Thesimultaneous multithreading feature in the POWER7 processor core allows the core toexecute instructions from two or four independent software threads simultaneously. Tosupport this feature, we use the concept of logical processors. The operating system (AIX,IBM i, or Linux) sees one physical processor as two or four logical processors if thesimultaneous multithreading feature is on. It can be turned off and on dynamically as theoperating system is executing (for AIX, use the smtctl command, and for Linux, use theppc64_cpu command). If simultaneous multithreading is off, each physical processor ispresented as one logical processor and thus only one thread.Shared dedicated modeOn POWER7 processor-based servers, you can configure dedicated partitions to becomeprocessor donors for idle processors they own, allowing for the donation of spare CPU cyclesfrom dedicated processor partitions to a shared processor pool. The dedicated partitionmaintains absolute priority for dedicated CPU cycles. Enabling this feature can help toPOWER HypervisorPhysical shared-processor poolDedicated processorpartitions Set of micro-partitions Set of micro-partitionsDedicated processorsShared-Processor Pool 0 Shared-Processor Pool 1AIX V6.11.5 PrU16-core SMP Systemvpvp vp vpKEY:vp virtual processorlp logical processorPrU Processing Unitslp lpvp vplp lplp lp lp lp lp lpAIX V5.30.5 PrUlp lp lp lplp lp lp lpIBM i V6.11.5 PrULinux0.5 PrUAIX V7.1AIX V5.3
