Consider a data center with an infinite number of servers. Each server has 1 uni

Question

Consider a data center with an infinite number of servers. Each server has 1 unit of CPU available. Three types of VMs (virtual machines) arrive to this system. VMs of type 1 request 1/2 unit of CPU each, VMs of type 2 request 1/4 unit of CPU each, and VMs of type 3 request 1/8 unit of CPU each. In each time slot, the number of VMs which arrive into the system is binomially distributed with parameters N and , and each VM is of type 1, 2, or 3, with probability 1/3 each. Consider the following two assignment policies. . FirstFit policy: assign the VM to the lowest indexed server which can accommodate it Update the available space in the server, once a VM is assigned to it. BestFit pllicy: assign the VM to the server with the least amount of space available (among all servers which have enough space to accommodate the VM). Update the available space in the server, once a VM is assigned to it VMs of type 1 stay in the system for a geometrically distributed amount of time with mean 10, VMs of type 2 stay in the system for a geometrically distributed amount of time with mean 8, VMs of type 3 stay in the system for a geometrically distributed amount of time with mean 30. Assume the following sequence of events in each time slot: departures occur first, then arrivals occur, followed by assignment of VMs to servers ·Assume 0.9. For different values of N, N = 22, N = 23, N-24, and N = 25, compute the average number of servers used by simulating FirstFit policy for 10 time slots ·Assume 0.9. For different values of N, N = 22, N = 23, N-24, and N = 25, compute the average number of servers used by simulating BestFit policy for 105 time slots . Plot the average number of servers versus N under two policies, respectively. (in one plot) Note: 1. As mentioned in class, please do the programming assignment in groups of two 2. Choose one programming language to do the simulation from C/C++, Matlab, Python, Java, and R. 3. Report should include the plot, simulation code, and annotations

Explanation / Answer

A virtual CPU (vCPU) also known as a virtual processor, is a physical central processing unit (CPU) that is assigned to a virtual machine (VM).

By default, virtual machines are allocated one vCPU each. If the physical host has multiple CPU cores at its disposal, however, then a CPU scheduler assigns execution contexts and the vCPU essentially becomes a series of time slots on logical processors.

Because processing time is billable, it is important for an administrator to understand how his cloud provider documents vCPU usage in an invoice. It is also important for the administrator to realize that adding more vCPUs will not automatically improve performance. This is because as the number of vCPUs goes up, it becomes more difficult for the scheduler to coordinate time slots on the physical CPUs, and the wait time can degrade performance.

In VMware, vCPUs are part of the symmetric multi-processing (SMP) multi-threaded compute model. SMP also allows threads to be split across multiple physical or logical cores to improve performance of more parallel virtualized tasks. vCPUs permit multitasking to be performed sequentially in a multi-coreenvironment.

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