"I wish it need not have happened in my time," said Frodo.
"So do I," said Gandalf, "and so do all who live to see such times. But that is not for them to decide. All we have to decide is what to do with the time that is given, us."
—The Fellowship of the Ring , Book 1, Chapter 2
Benchmarking programs is a common task that drives decisions about where and how to invest the effort of software developers. This task can be very simple to very complex, depending on desired accuracy and the kind of code being profiled. In an OS, code that is run very infrequently or at a low priority doesn't need to be validated to as high a standard as code that runs very frequently (such as the system timer interrupt handler) or at high priority (such as real-time priority). Benchmarking in userspace serves as an introduction to the concepts behind benchmarking in the kernel, and it allows us to measure the impact of the kernel on userspace performance.
In this studio, you will:
Please complete the required exercises below, as well as any optional enrichment exercises that you wish to complete.
As you work through these exercises, please record your answers, and when finished email your results to firstname.lastname@example.org with the phrase Userspace Benchmarking in the subject line.
Make sure that the name of each person who worked on these exercises is listed in the first answer, and make sure you number each of your responses so it is easy to match your responses with each exercise.
time. This is actually a special command built into the bash shell, so its documentation can be found under
man bash. As the answer to this exercise, use this command to make a few timings of the test programs and copy the results here.
timecommand outputs three different timings. List them here and explain the difference.
realtimings? Explain your observations.
time ./dense_mm 400
time ./parallel_dense_mm 400
systimings? Look at the code in
sing.cand explain your observations.
time ./sing 1000
clock_getres. You can access the documentation for this function in the manual pages:
man clock_getres. Warning: Internet versions of man pages are often not up to date. Use the version on your machine.
Look through the clocks available at the
clock_getres man page.
For this exercise, give two clock names. For the first, give a clock that would
be well suited for userspace benchmarking, and explain why. For the second,
give a clock that would be poorly suited for userspace benchmarking, and
clock_getresto write a short program called
getres.cthat gives the resolutions for several different clock types. This function requires using a structure called a
timespecwhich is also documented at the same man page, and is the basic data structure used to report timing information from the kernel to userspace.
As the answer to this exercise, copy and paste your program output.
Include at least one
_COARSE clock type.
clock_gettimeto figure out how long a call to
clock_gettimetakes. As the answer to this exercise, report this value.
parallel_dense_mm.c. First modify it so that you time the critical computational loop with the clock
CLOCK_MONOTONIC_RAW. Then modify it again so that the program takes a second parameter and executes the timed segment multiple times. Your program should output the minimum, average, and maximum timings over all timed iterations.
Leave the answer to this exercise blank
In addition to the answers above, please submit: