Why are ruby processes at 100% CPU on passenger

Question

I have a rails app (2.3.5) running on a VPS with 4 cores @ 2 GHz and 4GB memory. I am running nginx (0.7.61) and phusion passenger(2.2.14) on Ruby Enterprise (1.8.7-2010.01) with the max pool size set at 30. My problem is that it seems as if every ruby process that is executing a rails request runs at near 100% cpu. If I run TOP they drop off every time the display refreshes so they are not getting hung, but they are still running at 100%.

Is there any way I can bring this down? Or at least figure out what portion of code is spiking the CPU? Is this a normal behavior?

Here is the TOP output:

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                     
 2427 psadmin   25   0 91904  76m 2696 R  100  1.9 739:05.96 Rails: /var/www/apps/main_rails_app/current                                                                                                  
 3457 psadmin   25   0 98180  82m 2532 R  100  2.0 711:21.91 Rails: /var/www/apps/main_rails_app/current                                                                                                  
 2415 psadmin   25   0 93952  77m 2708 R   99  1.9 727:49.31 Rails: /var/www/apps/main_rails_app/current                                                                                                  
 3455 psadmin   25   0 99204  83m 2528 R   69  2.0 726:04.70 Rails: /var/www/apps/main_rails_app/current                                                                                                  
 2791 psadmin   16   0 98044  81m 2492 S   31  2.0   0:10.16 Rails: /var/www/apps/main_rails_app/current                                                                                                  
 8034 psadmin   15   0  8160 3656 1772 S    1  0.1   0:35.39 nginx: worker process                                                                                                                        
 8035 psadmin   15   0  8324 3696 1732 S    0  0.1   0:31.34 nginx: worker process                                                                                                                        
 2588 psadmin   15   0  197m 183m 2712 S    0  4.5   1:02.16 Rails: /var/www/apps/main_rails_app/current      

Thanks!

Edit: Tried strace with follow forks as mentioned below. This is the output that is dumped over and over:

sudo strace -f -p 3455

clock_gettime(CLOCK_MONOTONIC, {394577, 508326476}) = 0
select(0, [], [], [], {0, 0})           = 0 (Timeout)
--- SIGVTALRM (Virtual timer expired) @ 0 (0) ---
sigreturn()   

Answer 1

check your logs for suspicious behavior. In general rails does suck a bunch of cpu though...you could also try pointing strace at the offending pids.

Answer 2

Hi, I'm having the same issue on two different servers using:
Rails 2.3.5
passenger 2.2.5
ruby 1.8.7 (2009-12-24 patchlevel 248) [x86_64-linux], MBARI 0x6770, Ruby Enterprise Edition 2010.01

Do you know what the problem is and how to fix it?
Thanks.