Specifications

5102ch03.fm Draft Document for Review May 12, 2014 12:46 pm
88 IBM Power System S822 Technical Overview and Introduction
򐂰 The number of virtual processors can be changed dynamically through a dynamic
LPAR operation.
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
described in this section.
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 POWER8 processor core allows the core to
execute instructions from two, four or eight independent software threads simultaneously. To
support this feature consider the concept of
logical processors. The operating system (AIX or
Linux) sees one physical core as two, four or eight 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 core is presented as one
logical processor in AIX or Linux, and thus only one thread.
Shared dedicated mode
On POWER8 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
Set of micro-partitions
KEY:
vp Vi rtua l pro cessor
lp Lo gi ca l proce ssor
PrU Proce ssing U nits
Shared-Process or P ool 0
Set of micro-partitions
Shared-Processor Pool 1
lp lp lp lp lp lp lp lp lp lp lp lp
AI X V6. 1
1.5 PrU
AIX V5.3
0.5 Pr U
AIX V6.1
1.5 P rU
Linux
0.5 PrU
vpvp vp vpvp vp
lp lp lp lp lp lp
AI X V7. 1 AIX V6.1
Dedicated proc ess ors Dedicated processors
POWER Hypervisor
10-core SMP System