Advanced POWER Virtualization on IBM System p5 - Previous ...

Partition 2 is configured with one virtual processor and a capacity of 0.2
processing units, entitling it to 20 percent usage of a physical processor during
each dispatch interval. In this example, a worst case dispatch latency is shown
for this virtual processor, where the 2 ms are used in the beginning of dispatch
interval 1 and the last 2 ms of dispatch interval 2, leaving 16 ms between
processor allocation.
Note: It is possible for a virtual processor to be dispatched more than one time
during a dispatch interval. In the first dispatch interval, the workload executing
on virtual processor 1 in LPAR 1 is discontinuous on the physical processor
resource. This can happen if the operating system confers cycles, and is
reactivated by a prod hcall.
Hypervisor dispatch interval pass 1
Hypervisor dispatch interval pass 2
Physical
Processor 0
Physical
Processor 1
LPAR 1
VP 1
LPAR 2
VP 0
LPAR 3
VP 2
LPAR 1
VP 0
LPAR 1
VP 1
LPAR 3
VP 0
IDLE
LPAR 3
VP 1
LPAR 3
VP 2
LPAR 3
VP 0
LPAR 1
VP 0
LPAR 1
VP 1
LPAR 3
VP 1
IDLE
LPAR 2
VP 0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (ms)
LPAR1
Capacity entitlement = 0.8 processing units; virtual processors = 2 (capped)
LPAR2
Capacity entitlement = 0.2 processing units; virtual processors = 1 (capped)
LPAR3
Capacity entitlement = 0.6 processing units; virtual processors = 3 (capped)
Figure 2-10 Micro-Partitioning processor dispatch
Partition 3 contains three virtual processors, with an entitled capacity of 0.6
processing units. Each of the partition’s three virtual processors consumes
20 percent of a physical processor in each dispatch interval, but in the case of
virtual processor 0 and 2, the physical processor they run on changes between
dispatch intervals.
Processor affinity
The <strong>POWER</strong> Hypervisor is designed to dispatch threads on the same physical
processor as it ran on in the previous dispatch cycle. This is called processor
affinity. The <strong>POWER</strong> Hypervisor will always first try to dispatch the virtual
processor on the same physical processor as it last ran on, and, depending on
resource utilization, will broaden its search out to the other processor on the
<strong>POWER</strong>5 chip, then to another chip on the same MCM, then to a chip on another
52 <strong>Advanced</strong> <strong>POWER</strong> <strong>Virtualization</strong> on IBM System p5