AMX Rack Rail Kit MMS Servers Specifications download pdf (Page 94)

4405ch03 Virtualization.fm Draft Document for Review September 2, 2008 5:05 pm

80 IBM Power 570 Technical Overview and Introduction

Figure 3-1 Logical partitioning concepts

Dedicated mode

In dedicated mode, physical processors are assigned as a whole to partitions. The

simultaneous multithreading feature in the POWER6 processor core allows the core to

execute instructions from two independent software threads simultaneously. To support this

feature we use the concept of

logical processors. The operating system (AIX or Linux) sees

one physical processor as two 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, then each physical processor

is presented as one logical processor and thus only one thread at a time is executed on the

physical processor.

Shared dedicated mode

On POWER6 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 may 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 (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 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 should receive total CPU time equal to their processing units entitlement. The

logical processors are defined on top of virtual processors. So, even with a virtual processor,

the concept of logical processor exists and the number of logical processor depends whether

the simultaneous multithreading is turned on or off.

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AMX Rack Rail Kit MMS Servers Specifications Page 94