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Asked: 2026-06-03T00:50:23+00:00

I’ve got an auxiliary function that does some operations that are pretty costly. I’m

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I’ve got an auxiliary function that does some operations that are pretty costly.

I’m trying to profile the main section of the algorithm, but this auxiliary function gets called a lot within. Consequently, the measured time takes into account the auxillary function’s time.

To solve this, I decided to set and restore the time so that the auxillary function appears to be instantaneous. I defined the following macros:

#define TIME_SAVE struct timeval _time_tv; gettimeofday(&_time_tv,NULL);
#define TIME_RESTORE settimeofday(&_time_tv,NULL);

. . . and used them as the first and last lines of the auxiliary function. For some reason, though, the auxiliary function’s overhead is still included!

So, I know this is kind of a messy solution, and so I have since moved on, but I’m still curious as to why this idea didn’t work.
Can someone please explain why?

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1 Answer

  1. Editorial Team

    There are a couple possibilities that may be occurring. One is that Linux tries to keep the clock accurate and adjustments to the clock may be ‘smoothed’ or otherwise ‘fixed up’ to try to keep a smooth sense of time within the system. If you are running NTP, it will also try to maintain a reasonable sense of time.

    My approach would have been to not modify the clock but instead track time consumed by each portion of the process. The calls to the expensive part would be accumulated (by getting the difference between gettimeofday on entry and exit, and accumulating) and subtracting that from overall time. There are other possibilities for fancier approaches, I’m sure.

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