Specifications

132 IBM Power 770 and 780 Technical Overview and Introduction
Dedicated mode
In dedicated mode, physical processors are assigned as a whole to partitions. The
simultaneous multithreading feature in the POWER7 processor core allows the core to
execute instructions from two or four independent software threads simultaneously. To
support 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 the
simultaneous multithreading feature is on. It can be turned off and on dynamically while the
operating system is executing (for AIX, use the smtctl command). If simultaneous
multithreading is off, each physical processor is presented as one logical processor, and thus
only one thread.
Shared dedicated mode
On POWER7 processor technology-based servers, you can configure dedicated partitions to
become processor donors for idle processors that they own, allowing for the donation of
spare CPU cycles from dedicated processor partitions to a Shared Processor Pool. The
dedicated partition maintains absolute priority for dedicated CPU cycles. Enabling this feature
can help to increase system utilization without compromising the computing power for critical
workloads in a dedicated processor.
Shared mode
In shared mode, logical partitions use virtual processors to access fractions of physical
processors. Shared partitions can define any number of virtual processors (the maximum
number is 10 times the number of processing units assigned to the partition). From the
POWER Hypervisor point of view, virtual processors represent dispatching objects. The
POWER Hypervisor dispatches virtual processors to physical processors according to the
partition’s processing units entitlement. One processing unit represents one physical
processor’s processing capacity. At the end of the POWER Hypervisor’s dispatch cycle
(10 ms), all partitions receive total CPU time equal to their processing unit’s entitlement. The
logical processors are defined on top of virtual processors. So, even with a virtual processor,
the concept of a logical processor exists and the number of logical processors depends
whether the simultaneous multithreading is turned on or off.
3.4.3 Multiple Shared Processor Pools
Multiple Shared Processor Pools (MSPPs) is a capability supported on POWER7 processor
and POWER6 processor-based servers. This capability allows a system administrator to
create a set of micro-partitions with the purpose of controlling the processor capacity that can
be consumed from the physical Shared Processor Pool.