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Potpourri_1 Potpourri 1. [2 points] (Answer True/False with justification)  “SPIN and Exokernel are fair in comparing the superiority of their respective specialization approaches for OS services relative to Mach micro-kernel.” 

Potpourri_6b Potpourri The context for this question is the same as the previous question. 6. I/O ring data structures can be used to facilitate data transfer between paravirtualized guest OSs and the hypervisor. Consider a guest OS making a hypercall to the hypervisor to write some data to disk. The process begins with the guest making the write request, followed by the hypervisor processing the request and responding. Finally, the guest consumes this response.      b. [4 points] Access to the ring data structure is through several pointers. For the disk write, describe in order the sequence of pointer modifications from request production to response consumption. Assume that there is space in the I/O ring for the Guest OS to enqueue a new request. For each modification, state: who makes the modification (guest or hypervisor).  which pointer is modified.  what the pointer modification is. 

Parallel_Systems_8b LRPC The context for this question is the same as the previous question. 8. Consider a single processor machine running a client and server. The client calls a procedure ‘foo’ on the server with the following declaration:   void foo(data_structure a, data_structure b);     The server always expects the actual parameters of the call to be in its stack.     Consider the following variables representing average times to complete the described operations.  T1: Average time to copy a variable of type ‘data_structure’ from user space to kernel space and vice versa.  T2: Average time to copy a variable of type ‘data_structure’ from user space to user space.  T3: Average time the server takes to execute the procedure ‘foo’.  T4: Average time to switch between user-space domains (averaged over thread-doctored and normal thread-scheduled workflows).  T5: Average time for a kernel trap and associated validation (averaged over binding object and non-binding object workflows).     Answer the questions below based on the information and average times given above. You should give an explanation of the component times that make up your answer to get any credit. Consider any other time that is not mentioned above as negligible.    b. [3 points] Calculate the total client wait time after calling the procedure ‘foo’, if the server and client were two different processes, and the OS does not optimize the RPC workflow for processes running on the same machine. 

Potpourri_2 Potpourri 2.  [2 points] (Answer True/False with justification)  In a fully virtualized environment, the hypervisor uses the Physical Page Number (PPN) generated by the Guest Operating system to index into the Shadow Page Table and map it to the corresponding Machine Physical Number (MPN).

Parallel_Systems_4c M.E.Lock The context for this question is the same as the previous question. 4. Consider the following lock algorithm: while ((L == locked) or (T&S(L) == locked)) {    while (L == locked); // spin    delay (d[Pi]); // different delays for different processors  }  // success if we are here    c. [2 points] What are the program characteristics that would enhance the program’s performance with this lock algorithm implementation? In what way does it improve performance?

Parallel_Systems_5b M.E.Lock The context for this question is the same as the previous question. 5. Consider the ticket lock algorithm from lecture 4 (slide 108): b. [1.5 points] What are the downsides of the ticket lock algorithm for systems with write-update cache coherence? Briefly explain your answer.

Potpourri_6c Potpourri The context for this question is the same as the previous question. 6. I/O ring data structures can be used to facilitate data transfer between paravirtualized guest OSs and the hypervisor. Consider a guest OS making a hypercall to the hypervisor to write some data to disk. The process begins with the guest making the write request, followed by the hypervisor processing the request and responding. Finally, the guest consumes this response. Now consider an I/O ring that is used by a paravirtualized guest OS to send network requests and to receive corresponding responses. At time 0, the guest enqueues requests A, B, and C in that order. The hypervisor receives the responses corresponding to A, B, and C from the network at times shown in the table below:  Response ID  Time when response received by hypervisor  A  100 ms  B  10 ms  C  60 ms   Assume that it takes a negligible amount of time for the guest/hypervisor to enqueue requests/responses to the I/O ring.      c. [1 point] How long from time zero does it take for the first response to be available to the guest OS? 

Find the value of the polynomial for the given replacement value.4×2 – 4x + 30        for x = -2

Virtualization_3 Memory Management 3. [4 points] There are two guest OSes (OS1 and OS2) running on top of the hypervisor. Assume that vpn1 of OS1 and vpn2 of OS2 are mapped to the same machine page (mpn1) through VM oblivious page sharing. A process in OS2 attempts to write to vpn2.  List the actions that ensue as a result.

Virtualization_2 Full Virtualization 2. [4 points] In a fully virtualized environment, consider the following:  Two VMs are currently running. VM1 has 3 processes running; VM2 has 4 processes running.    Assume the size of the hardware page table is 1 MB.    What is the total memory overhead incurred by the Hypervisor for the above configuration? Show your work for any credit.