Processor Resources
With the core fabric of a virtual machine understood, it’s time to move on to the
processor, which is one of the most interesting and used resources for a virtual
machine. It’s important to understand some of the terminology related to processor
resources and how this relates to virtualization and Hyper-V.
There is a difference between the number of processors, cores, and logical processors
and the amount of memory supported by Windows Server and that supported by
Hyper-V. With new processors having multiple processing cores, and technologies
such as hyperthreading adding more complexity to understanding processors, a review
of logical and virtual processors is important.
Motherboards have one or more sockets, which can have processors installed. This is
why the terms socket and processor are sometimes used interchangeably. Each
processor has one or more processing cores. Early processors had only one core, but
multicore processors became predominant starting with dual-core processors, then
quad-core, and today there are 10-core processors available. Each core acts like a
separate processor with the ability to perform its own execution of program
instructions, though the cores share a common bus interface and certain types of
processor cache, as explained in Chapter 1.
In many types of program instruction execution, not all of the core’s execution
resources are utilized, so Intel introduced a hyperthreading technology. This
technology makes a single processor core look like two processor cores, known as
logical processors, and allows two instruction threads to run on each processor core.
This increases overall throughput by allowing the processor to switch between the two
instruction threads to keep the cores busy; it’s common for instruction threads to stall
while waiting on a resource. With hyperthreading, if one thread stalls, the other
thread can be executed. There is still only a single execution resource on the core, so
hyperthreading does not double performance; the improvement varies, but between a
10 to 15 percent performance improvement is an accepted value.
Figure 2.8 shows Task Manager on one of my Windows Server 2012 R2 boxes. It has
two Intel Xeon processors, which are eight-core processors, and has hyperthreading
enabled. Notice that the socket count is 2 and the core count is 16, while the logical
processor count is 32 because the hyperthreading splits each core into two logical
processors.