Minutiae: The Beginning

by Arav K. on

It may be somewhat masochistic, but making a single tiny aspect of my computer unnecessarily, almost stupidly efficient brings a strange joy to my heart. At this moment, the target of that obsession is my status bar. I dream of an age where my status bar updates itself exactly when necessary and never else. To that end, I’m going to write what could be the most efficient date/time printer ever.

I’ll lay out the exact goals here so that we can objectively measure my success. The end result of this journey will be a GNU C23 program for arbitrarily recent Linux kernels which periodically formats the current date and time and prints it as a single line to standard output. It will print a new line immediately after the current time changes from the user’s perspective (e.g. a minute passes, the timezone changes, etc.). I18N / L10N are explicit non-goals - I might hardcode date-time formatting logic for my own locale (effectively en_GB.UTF-8). Over time, I will refine this program to take as few system resources as possible – something we can measure in terms of CPU time and memory consumption.

Each post in this series will cover one or two improvements to the program, with explanations of the technologies used and benchmarks measuring the improvement. For a start, we’ll compare to the classic shell script:

while :; do
  date '+%A, %d %b %Y %H:%M'
  sleep 60

This also shows you the format string I’ll be working with. The output looks like this:

> ./minutiae.sh
Wednesday, 27 Dec 2023 09:51
Wednesday, 27 Dec 2023 09:52
Wednesday, 27 Dec 2023 09:53
Wednesday, 27 Dec 2023 09:54

Let’s see if I can benchmark this. For fairness, I’ll run the script using dash rather than bash – it’s more lightweight and we don’t need any extra features anyways. Using perf stat for some overall information:

> perf stat ./minutiae.sh
 Performance counter stats for './minutiae.sh':

            765.46 msec task-clock:u                     #    0.000 CPUs utilized
                 0      context-switches:u               #    0.000 /sec
                 0      cpu-migrations:u                 #    0.000 /sec
            39,859      page-faults:u                    #   52.072 K/sec
       207,468,145      cycles:u                         #    0.271 GHz
       141,723,023      instructions:u                   #    0.68  insn per cycle
        30,836,134      branches:u                       #   40.284 M/sec
         2,269,916      branch-misses:u                  #    7.36% of all branches

   17138.888268817 seconds time elapsed

       0.481000000 seconds user
       0.350438000 seconds sys

This is surprisingly efficient! Over 268 minutes of runtime (not counting time suspended), less than a second of CPU time was spent. I’m reasonably certain that this is counting the overhead of all the programs involved: dash, date, and sleep. But minutiae.sh is not perfect. Not by a long shot.