Measuring a process context switch

Question

I am creating a C program to measure a process switch for a project, and I am having a couple difficulties. The method I am using is to create 2 pipes, parentpipe and childpipe. The parent writes one byte in to its pipe then reads the child pipe, theoretically forcing control to the child pipe. The child e reads the parent pipe and writes a byte to the child pipe.

Here are my issues:

1. The processes aren't actually forced to switch. If I use sleep instead of the above method then they switch, but I'm trying not to use sleep. How do i force them to switch?

2. I am using CLOCK_MONOTONIC to measure and can't figure out where to put the start and stop for it. I keep getting junk values no matter where I put them (assuming I put one in each process:start in one and stop in the other). Where do i put the clocks?

Thank you for your help.

Answer 1

1. Be sure to select unbuffered i/o. Otherwise read and write wait for more characters before returning, even when only one byte is requested.

2. Record CLOCK_MONOTONIC at the beginning of the program and subtract it from all subsequent timestamps. Typically CLOCK_MONOTONIC is implemented as the time since the system booted. Suggesting where to put the measurement would be easier if you showed your code.