Comp150CPA: Clouds and Power-Aware Computing
Classroom Exercise 7
Load and response time
Spring 2011

group member 1: ____________________________ login: ______________

group member 2: ____________________________ login: ______________

group member 3: ____________________________ login: ______________

group member 4: ____________________________ login: ______________

group member 5: ____________________________ login: ______________

In class we have studied the linkage between request service time and the concept of load average. Let's explore that issue in more detail.

  1. Suppose that in 10 time intervals, there are two processes running. Process 1 computes during intervals 3 and 4, while process 2 starts at interval 4 and computes during intervals 5, 6, and 7. What is the load average over 10 intervals?

  2. Suppose you have 10 time intervals on a single-core machine wherein three processes are running. Assume that for any time interval, a single process is either be computing, ready to run, or waiting for something else. Give a time-space diagram with three processes on Y and 10 time intervals on X that depicts a situation with a load average of 1.5 over the 10 time intervals.
  3. Depict your schedule from problem 2 again, but this time, simulate what would happen if you replaced your 1-core machine with a 2-core machine; in other words, two processes can be "computing" at a time. What is the new load average?

  4. Depict your schedule from problem 2 again, but this time, depict what would happen running on a virtual server with 50% of the physical server (half the time, another operating system instance is running). What is the load average now?

  5. (Advanced) In class we noted that load L is "roughly" proportional to service time W. The reason we did not claim exact proportionality is that operating systems do other things than just responding to service. This results in two kinds of "overhead": overhead related to each request, and overhead necessary for running the operating system that has nothing at all to do with requests. Adding overhead to the picture, what is the real relationship between L and W?