IBM Power 750 Technical Overview And Introduction page 139

Processing mode
When you create a logical partition you can assign entire processors for dedicated use, or you
can assign partial processing units from a shared processor pool. This setting defines the
processing mode of the logical partition.
Figure 3-7 shows a diagram of the concepts discussed in this section.
lp lp lp lp lp lp
Dedicated processors
Figure 3-7 Logical partitioning concepts
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
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; for Linux, use the
ppc64_cpu --smt 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.
Set of micro-partitions
lp lp lp lp lp lp
vp vp vp
Shared-Processor Pool 0
POWER Hypervisor
Dedicated processors
8-core SMP System
logical processors
Set of micro-partitions
lp lp lp lp lp lp
vp vp vp
Shared-Processor Pool 1
KEY:
vp Virtual processor
lp Logical processor
PrU Processing Units
. The operating system (AIX,
Chapter 3. Virtualization
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