set to 50 percent, then it means that half of one of the logical processors is always
available to this virtual machine. Note that it does not mean it’s the same core or all
from the same core, but the hypervisor will ensure that the virtual machine always
has the equivalent of half of a logical processor of processing available to this
virtual machine. If the virtual machine is not using the full reserve, other virtual
machines may access the processor resource. However, as soon as the virtual
machine with the reserve needs the CPU, it will take priority and be guaranteed its
full allocation. The Percent Of Total System Resources value shows what
percentage of the overall system resources the reserve that’s assigned equates to. If
a virtual machine has been assigned 8 virtual processors with a 25 percent reserve
and the server has 16 logical processors in total, this means that the percent of total
system resources reserved is 12 percent ( 12. 5 percent, really).
Virtual Machine Limit (Percentage) The maximum amount of processor that
the virtual machine can use. The default is 100 percent, which means that this
virtual machine can use the entire resources of the allocated processors. Note that
in times of resource contention, the virtual machine may not get a full 100 percent,
but it will always get its reserve amount.
Relative Weight Used to determine the importance of a virtual machine getting
shares of the CPU time in times of resource contention. For example, a virtual
machine with a weight of 200 would get twice the number of CPU cycles that a
virtual machine with a weight of 100 would get.Although the number of processors of a virtual machine cannot be changed after the
virtual machine has been started, it is possible to modify the Virtual Machine Reserve
(Percentage), Virtual Machine Limit (Percentage), and Relative Weight values while
the virtual machine is running. This enables you to tweak processor resources for a
virtual machine dynamically. This would let you assign extra processors to a virtual
machine than normally would be required, but you can set the Virtual Machine Limit
(Percentage) value to something like 50 percent so that only half the capacity could be
used. If more processor is required while the virtual machine is running, that value
can be increased. Typically, operating systems will not “waste” processor resources, so
this type of limiting usually is not required, unless you have a heavily overcommitted
system or a virtual machine with rogue processes.
SOLVING “HANGING” PROBLEMS FOR VERY LARGE HYPER-V
VIRTUAL MACHINES
For a virtual machine with more than 32 virtual processors, I would sometimes
see the virtual machine hang within 30 seconds of logging on (the same time
Server Manager started and used processor resources). After investigation, I
found that the problem was that a large number of the logical processors in the
Hyper-V host had gone into a C 3 sleep state, which is a deep sleep state to save
power when the processor is idle. The problem seemed to be caused by all of these