OPcache compilation performance regression in PHP 5.6/7 with huge classes
| From: | David Zuelke | Date: | Tue, 14 Mar 2017 10:29:59 +0000 |
| Subject: | OPcache compilation performance regression in PHP 5.6/7 with huge classes | ||
| Groups: | php.internals | ||
| Request: | Send a blank email to internals+get-98517@lists.php.net to get a copy of this message | ||
Hi all,
There appears to be a performance regression in the CFG and DFA based optimization passes of OPcache
in PHP 5.6+ when loading huge classes (such as those generated by Symfony's routing component)
for the first time.
The issue does not occur on PHP 5.5. Tests below are with 5.6.30, 7.0.16 and 7.1.2 and default INI
settings; I replicated the issue on both macOS and Linux.
Test file here (it's from an actual application, slightly anonymized, not a synthetic example):
https://gist.github.com/dzuelke/fe867f55f09e0bf79ecefcc815b7fe92
Without OPcache, everything is fine in all versions:
$ time -p php -dopcache.enable_cli=0 hugeclass.php
real 0.10
user 0.09
sys 0.00
With OPcache on, things are suddenly much, much slower:
5.6:
$ time -p php -dopcache.enable_cli=1 hugeclass.php
real 3.23
user 3.21
sys 0.02
7.0:
$ time -p php -dopcache.enable_cli=1 hugeclass.php
real 1.76
user 1.73
sys 0.02
7.1:
$ time -p php -dopcache.enable_cli=1 hugeclass.php
real 4.01
user 3.98
sys 0.02
For comparison, 5.5 is as speedy as you'd expect it to be:
$ time -p php -dopcache.enable_cli=1 hugeclass.php
real 0.14
user 0.11
sys 0.02
If we switch off optimization passes 5 (CFG based) and 6 (DFA based, only in 7.1), everything is
great again in all versions:
$ time -p php -dopcache.enable_cli=1 -dopcache.optimization_level=0x7FFFFFCF hugeclass.php
real 0.13
user 0.10
sys 0.02
For 5.6 and 7.0, pass 6 is not a thing, but in 7.1, we can inspect passes 5 and 6 separately.
Pass 5 (CFG based) already makes for a drastic performance hit in 7.1:
$ time -p php -dopcache.enable_cli=1 -dopcache.optimization_level=0x7FFFFFDF hugeclass.php
real 0.88
user 0.86
sys 0.01
But pass 6 (DFA based) is the one that causes the biggest slowdown in 7.1:
$ time -p php -dopcache.enable_cli=1 -dopcache.optimization_level=0x7FFFFFEF hugeclass.php
real 3.29
user 3.24
sys 0.04
In all versions, subsequent loads from the cache (such as when running FPM or the built-in web
server) are fast.
Is this slowness with a cold cache expected/accepted, or does that qualify as a bug?
David