0002186: microtime() is only millisecond-accurate - Mantis

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ID

Category

Severity

Reproducibility

Date Submitted

Last Update

0002186

[Quercus]

minor

always

11-18-07 15:06

11-19-07 20:16

Reporter

koreth

View Status

public

Assigned To

nam

Priority

normal

Resolution

fixed

Status

closed

Product Version

3.1.4

Summary

0002186: microtime() is only millisecond-accurate

Description

I was doing some performance tests in compiled mode and noticed my run times had much less noise than expected:

<?php
$start_time = microtime(true);
include_once $_SERVER['PHP_ROOT'].'/lib/core/init.php';
print "elapsed = " . (microtime(true) - $start_time) . " sec\n";

elapsed = 0.006000041961669922 sec
elapsed = 0.003000020980834961 sec
elapsed = 0.0029997825622558594 sec
elapsed = 0.003000020980834961 sec
elapsed = 0.003000020980834961 sec
elapsed = 0.003000020980834961 sec
elapsed = 0.003000020980834961 sec
elapsed = 0.003000020980834961 sec
elapsed = 0.002000093460083008 sec
elapsed = 0.003000020980834961 sec

The Zend PHP interpreter is much more accurate. This lack of precision makes it much harder to do meaningful internal performance monitoring in a PHP app -- and in particular, to benchmark Quercus versus vanilla PHP and identify their respective bottlenecks -- since most operations will appear to take either no time at all or 1 millisecond depending on whether they happen to straddle a millisecond boundary.

Additional Information

patch.txt [^] (1,509 bytes) 11-18-07 15:41

Relationships

Notes
(0002505) koreth 11-18-07 15:37	Simpler test case: <?php $a = microtime(true); for ($i = 0; $i < 10; $i++) ; $b = microtime(true); print ($b - $a) . "\n"; You'll get "0.0" from Quercus nearly every time you run this, and various small numbers from vanilla PHP.

(0002506) koreth 11-18-07 15:45	One possible fix attached; on Linux, at least, System.nanoTime() actually returns the nanosecond-accurate system time. Since that's not guaranteed by the JDK spec I test to see if it's true, and if not, fall back to the old behavior. A more robust implementation would probably try to figure out the offset between nanoTime() and currentTimeMillis()*1000000, but this is at least better than the current situation.

(0002511) nam 11-19-07 20:16	php/1903 System.nanoTime() returns the system time for Linux machines System.nanoTime() returns some arbitrary timer time for Windows machines microtime() changed to return System.nanoTime() for non-windows machines, and System.currentTimeMillis() for windows

Issue History
Date Modified	Username	Field	Change
11-18-07 15:06	koreth	New Issue
11-18-07 15:37	koreth	Note Added: 0002505
11-18-07 15:41	koreth	File Added: patch.txt
11-18-07 15:45	koreth	Note Added: 0002506
11-19-07 20:12	nam	Status	new => assigned
11-19-07 20:12	nam	Assigned To	=> nam
11-19-07 20:16	nam	Status	assigned => closed
11-19-07 20:16	nam	Note Added: 0002511
11-19-07 20:16	nam	Resolution	open => fixed
11-19-07 20:16	nam	Fixed in Version	=> 3.1.4

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