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Date: Tue, 27 Sep 2016 09:08:13 +0200
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Subject: How to get zval map to identify cpu hog?
From: thomas.lamy@netwake.de (Thomas Lamy)

Hi,

it's the second time I'm running into this: In a rather big project I'm 
using gearman to enable semi-parallel processing of many small jobs. I'm 
using PHP 5.6.22-0+deb8u1 with OPcache 7.0.6-dev on Debian.

All was well before the code needed refactoring for a new feature: 30 
workers processed 4000 jobs/second at around 5% CPU usage.
After refactoring (no functional changes), some times after starting the 
workers, processing is getting slower and slower. After about 2 hours I 
hit 100% CPU usage, at about 300 jobs/second.

Memory usage only doubles from start to stall, which is what I observed 
before when everything was fine.


I suspect this to be a problem of the cycle collector, or with garbage 
collecting in general. So at any given time, I want PHP to dump all the 
zval's around, which I have to evaluate manually to find "problematic" 
ones. This could be triggered by either a function call, or by 
adding/extending PHP's signal handler and sending that signal to the 
interpreter process.

Where do I have to look at in the sources? Or is there already a tool 
which does what I want, but didn't find yet?


I also learned this _could_ be hash collisions related to reordering and 
renaming the data in my code, but as I'm currently stuck with 5.6 I 
can't use the HashDoS related patches floating around here.


Any hints on where to find the culprit?


Thanks,

   Thomas