ECEn 324 Homework Set #5

Submit your (hardcopy) solutions to the problems below in the homework box by 5:00 PM on the assigned date.

  1. Click here to get the source code to a simple cache simulator that is incomplete. Your assignment is to provide the missing code at each of the 3 points marked by the comment "// Your code goes here". You should be able to figure out what is needed by studying the remaining code and the comments. Test your code by simulating the cache with the default cache configuration (2-way associative, 128-byte cache, 4-byte blocks) and the default reference sequence in the cachesim.c file. The cache is small enough and the reference sequence short enough that you should be able to hand-verify the correctness of your results.
    When you are confident that your code works on the initial test case, run the simulator on two additional cache configurations and reference sequences of your choosing. Imagine that you are part of a team tasked to test this code. Pick two quite different cache configurations, and for each carefully devise a reference sequence that you think constitutes a good test of its correctness. (The reference sequence need not be lengthy -- they don't need to exceed about 20 references.) If you find a bug, be sure to report it!

  2. Problem 6.39 from the text.

  3. Problem 6.40 from the text.

  4. Click here to get a tar file with some source code that you just analyzed for problems 6.39 and 6.40 from the text. Let's see what we can learn from running similar code on a real machine. Typing "make" in the cacheperf directory should produce a "cacheperf" executable that you can run. Look through the source code of "cacheperf.c" to see what it does. Note that, for each of the three code portions measured, the program outputs both raw cycle counts and summaries of relative run time, where the base length is the run time with a warm cache and good locality. The results obtained by running the program should give us insight into (a) performance differences between cold and warm caches, and (b) performance differences between access patterns with good and poor locality. You should recompile and run the program from a wide variety of SQSIZE values (in "cacheperf.c"). Include one or more tables of results, and write a paragraph that answers the questions below, along with anything else you observed that is noteworthy.

  5. Create a memory mountain for at least one machine that you have access to. Click here to get a tar file for code to compute the memory mountain. The code should compile and run on most Linux and Macintosh systems. Look through the code in mountain.c to see how it works. When you run the program, it should create a "mountain.res" file of resulting throughput values that you can examine. The tar file includes a "mountain.xlsx" Excel file set up to compute the memory mountain surface. On a machine with Excel (you can use the college machines in the computer room), open the "mountain.res" file, then cut and paste the values to the worksheet in "mountain.xlsv".
    Write a paragraph about your results that answers the questions below, along with any other observations you'd care to make.

  6. Problem 7.12

  7. Let's try to construct an example where the actions of the linker create an "insidious run-time bug" (p. 665). Start with the code in this tar file. The Makefile compiles files "intdblconf1.c" and "intdblconf2.c" to produce the executable "intdblconf". As the file names suggest, the two files have conflicting definitions for a particular variable, declared in one file as an int and in the other as a double. Look through the source code, see what it does, and what the output means. Edit the source code and change the initialization of variable x to experiment with different weak and strong symbol scenarios. Try at least one different computer platform if you can, and experiment with different optimization levels in the Makefile. Also, make particular note of warning or error messages you get from the linker. Write a paragraph that summarizes what you found. What is the nature of the insidious run-time bug you discovered, and what is required to produce it? Does the linker help us out in avoiding these kinds of problems with a suitable warning message?

Clarifications

For problem 1, include the source code from your main() function (with your code additions). Include the output of the simulator for the initial cache configuration. For each of your two new configurations, include the program output detailing the cache parameters, the reference sequence, and the outcome. For each configuration, say something about how you chose the reference sequence, the characteristics of your cache organizations that they test, and how you know that the simulator is correct.

For problems 2 and 3 (6.39 and 6.40), no programming or source code is required.

For problem 4, no source code need be included in your submission. Think through the results you report until you feel that you can explain them.

For problem 5, no source code is required in your submission, but you should include a printout of the memory mountain (the graph from the Excel spreadsheet) along with your written comments about that surface and what you can deduce from it. Even though this version of the memory mountain code makes repeated measurements of each data point, the accuracy of the results can vary widely with the system load; try to run it on a machine that is otherwise mostly idle. (Try running "top" to check the load average and CPU-intensive processes that might be running in the background.) Finally, you really should try this on different types of machines if you can -- the differences in the surface can be startling. Mention in your report if you made memory mountains on multiple platforms.

For problem 6 (7.12), the problem is asking you to identify the line number, the address of the starting byte the label represents, and the value contained in memory starting at that location as seen from the linked file (Fig 7.10).
No programming or source code is required for problem 7.12.

For problem 7, include source code and a screenshot of the output that clearly shows one instance where the bug arises, and explain the bug in your writeup.


Last updated 2 May 2013