CODEWITHSUNDEEP
clinux
Sachin Sharma
Sachin Sharma

Reputation: 31

Time to run instructions of a for loop

I am interested to calculate a duration of 125 μs for implementing a TDM (Time Division Multiplexing scheme) based scheme. However, I am not able to get this duration with an accuracy of +-5us using the Linux operating system. I am using DPDK which runs on ubuntu and intel hardware. If I take time from the computer using function clock_gettime(CLOCK_REALTIME), it adds the time to make a call to the kernel to get the time. This gives an inaccurate duration to me.

Therefore, I dedicated a cpu core for calculating time without asking the time from the kernel. For this, I run a for loop for a maximum instructions (8000000) and find the number instructions that need to be executed for the 125 μs duration (i.e. (125*8000000)/timespent).

However, the problem is that it is also giving inaccurate results (there is always different results i.e., a difference 1000 instructions).

Upvotes: 0

Views: 110

Answers (1)

Francois Girard
Francois Girard

Reputation: 348

You are getting inaccurate result because you are on a multitasking operating system. You cannot do this on modern computers. You can only do this on embedded microcontroller where you control 100% of the cpu time. The operating system need to manage your process, even if you have a dedicated cpu. The mouse and keyboard takes time also. Your have to run the process on 'Bare Metal'.

Upvotes: 1

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