Why was a BogoMip bogus?

I woke up this morning wondering something I hadn't in years. Why was Linux' BogoMip bogus?

I first installed Slackware Linux from a huge stack of 3.5" floppy disks. My life was changed. This was in the 1.0.X kernel days.

I stopped dicking around with Linux as my desktop OS when OS X bridged the gap. I have not made zlilo in over 2 decades, but this morning I woke up wondering about BogoMips!?

BogoMips were the computing speed measurement of note at my first internet start-up, an ISP and datacenter, and every new Intel or Intel-compatible CPU was curiously investigated by our tech team. When we'd boot a Linux kernel, we would watch carefully to see "the number of million times per second a processor can do absolutely nothing".

This morning I had to know! What the hell was so bogus about a BogoMip?

Linux Journal's Wim van Dorst answered that question 23 years ago!

Some device drivers in the Linux kernel need timing delays. Either they need a very short delay, or the delay must be very accurately determined. A simple non-busy loop cannot do this. Therefore, Linus Torvalds added a calibration in the boot procedure to predetermine how often a specific busy-loop algorithm can be calculated in one second. This predetermined value, called loops_per_second, is used in the device drivers to delay for precisely measured times.

For fun, Linus also added a print statement presenting this predetermined value (divided by 500,000) as BogoMips. Linus apparently loves it when millions of Linux users are gazing at their computer, baffled by these bogus MIPS.

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