Mike Mike - 1 year ago 96
C Question

How can I programmatically find the CPU frequency with C

I'm trying to find out if there is anyway to get an idea of the CPU frequency of the system my C code is running on.

To clarify, I'm looking for an abstract solution, (one that will not be tied to a specific architecture or OS) which can give me an idea of the operating frequency of the computer that my code is executing on. I don't need to be exact, but I'd like to be in the ball park (ie. I have a 2.2GHz processor, I'd like to be able to tell in my program that I'm within a few hundred MHz of that)

Does anyone have an idea use standard C code?

Answer Source

How you find the CPU frequency is both architecture AND OS dependent, and there is no abstract solution.

If we were 20+ years ago and you were using an OS with no context switching and the CPU executed the instructions given it in order, you could write some C code in a loop and time it, then based on the assembly it was compiled into compute the number of instructions at runtime. This is already making the assumption that each instruction takes 1 clock cycle, which is a rather poor assumption ever since pipelined processors.

But any modern OS will switch between multiple processes. Even then you can attempt to time a bunch of identical for loop runs (ignoring time needed for page faults and multiple other reasons why your processor might stall) and get a median value.

And even if the previous solution works, you have multi-issue processors. With any modern processor, it's fair game to re-order your instructions, issue a bunch of them in the same clock cycle, or even split them across cores.

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