[php-src] Issue #9084: usleep has 50µs+ overhead

Issue: https://github.com/php/php-src/issues/9084 Author: terwey ### Description During some benchmarking I noticed that usleep() adds roughly 54µs overhead to each call even when the time is set to 0. If usleep(5) is called the call takes 60µs, the ~55µs is always added on top. I have checked if this is just an overhead for a function but it cannot be reproduced with e.g. a sqlite3 call (those are sub 3µs). The overhead was a bit lower on different platforms with different PHP versions, but still very present. These numbers are from a machine with a AMD Ryzen 7 3700X 8-Core Processor. 3v4l.org link: https://3v4l.org/laINg#v8.1.5 (I have lowered the $revs due to timeout). The following code: ```php <?php $revs = 1000000; $time_start = microtime(true); for ($n=0; $n<$revs; $n++) { usleep(0); } $time_end = microtime(true); $time = $time_end - $time_start; echo "$time seconds\n"; $ops = ($time * 1000 * 1000) / $revs; echo "$ops op/microsecond"; ``` Resulted in this output: ``` 54.799515008926 seconds 54.799515008926 op/microsecond ``` But I expected this output instead (or similar): ``` 0.76021695137024 seconds 0.76021695137024 op/microsecond ``` ### PHP Version PHP 8.1.5 ### Operating System Debian