Software Environments - Heterogeneous Multicore Processor Technologies for Embedded Systems - page 167

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Fig. 5.9 Logical partitioning

to partition-configuration commands. Once a partition is configured, the operat-
ing systems are loaded into each partition, and a domain on each partition starts
to run the operating system and applications. The partition controller checks
every access request for hardware resources that the operating system and appli-
cations generate and invalidates any unauthorized requests.
Failure isolation and predictable resource allocation are the two most important
goals of physical partitioning. Although physical partitioning sacrifices flexibility in
allocating resources to partitions to achieve these goals, it is generally easy to imple-
ment with hardware and imposes little overhead on application execution.

5.2.4.2 Logical Partitioning

With logical partitioning, domains share some physical resources, usually in a time-
multiplexed manner. Thus, logical partitioning makes it possible to run multiple
operating system images on a single hardware system, which enables dynamic
workload balancing. Logical partitioning is used to implement virtual machines on
PC servers and mainframes to optimize utilization of hardware resources.
Logical partitioning is more flexible than physical partitioning but requires
additional mechanisms to provide the services needed to share resources safely and
efficiently. Usually, a hypervisor —that is, a programming layer lower than the
operating system and hidden from general system users (see Fig. 5.9 )—controls
each partition's configuration. When the system boots up, the hypervisor sets up
the hardware resources for use in a partition according to the partition-configuration
commands. Once a partition is configured, the hypervisor loads the operating sys-
tems and applications into each partition, and a domain on each partition starts to
run them. During the execution of the operating system and applications on the