IBM PS700, Technical Overview And Introduction

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Chapter 3. Virtualization
87
Figure 3-3 Concepts on dedicated and shared processor modes
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 as the
operating system is executing (for AIX, use the
smtctl
command, and for Linux, use the
ppc64_cpu
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-based servers, you can configure dedicated partitions to become
processor donors for idle processors 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 use, without compromising the computing power for critical workloads in a
dedicated processor.
Dedicated Processor
Set of Micropartitions
POWER Hypervisor
Physical Shared Processor Pool
Shared Processor Pool
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