processors still carries some overhead, but it is fairly minimal and has nowhere near
the impact of a hypervisor that uses gang scheduling. In my lab environment, nearly
all my virtual machines have two processors, and some have eight.
Using the same dinner analogy for Hyper-V would allow you to order dinner whenever
you were ready and then get your food. This would be, however, poor dining etiquette
on your part and would likely get you excluded from future dinner events and subject
you to lots of future solo dining.
The exact number of virtual processors supported for each guest operating system for
Hyper-V is documented and updated at
https://technet.microsoft.com/library/mt126119.aspx, but the primary numbers are
shown in Table 2.2. Note that Windows Server 2000 and Windows Server 2003 are
not listed on the Microsoft site because they are no longer supported operating
systems; only one processor was supported for Windows Server 2000 and two for
Windows Server 2003.
Table 2.2: Maximum Number of Virtual Processors
OPERATING SYSTEM NUMBER OF VIRTUAL
PROCESSORS
Windows Server 2008 R2 and above 64
Windows Server 2008 SP2 4
Modern supported Linux distributions (RHEL 5.9+,
SUSE 11 SP2+, Ubuntu 12.04+)64
Windows 8 and above 32
Windows 7 4
Windows Vista SP2 2It’s important to understand that gang scheduling is not bad; rather, there’s just not
an efficient algorithm to use it at this time. In the future, a perfect algorithm may be
created, and then I would not be surprised to see Hyper-V implement some type of
gang scheduling.
Processor Assignment
When assigning processors to a virtual machine, between 1 and 64 (or the number of
logical processors in the system) can be assigned. Additionally, it is possible to set
three other values that help control the processor resource usage. These are Virtual
Machine Reserve (Percentage), Virtual Machine Limit (Percentage), and Relative
Weight:
Virtual Machine Reserve (Percentage) The amount of the processor that is
reserved for this virtual machine and therefore always available. If a host has 4
logical processors and the virtual machine has 1 virtual processor and the reserve is