W3WP.EXE using 100% CPU - where to start?

Question

An ASP.NET web app running on IIS6 periodically shoots the CPU up to 100%. It's the W3WP that's responsible for nearly all CPU usage during these episodes. The CPU stays pinned at 100% anywhere from a few minutes to over an hour.

This is on a staging server and the site is only getting very light traffic from testers at this point.

We've running ANTS profiler on the server, but it's been unenlightening.

Where can we start finding out what's causing these episodes and what code is keeping the CPU busy during all that time?

Answer 1

If your CPU is spiking to 100% and staying there, it's quite likely that you either have a deadlock scenario or an infinite loop. A profiler seems like a good choice for finding an infinite loop. Deadlocks are much more difficult to track down, however.

Answer 2

This is a very old post, I know, but this is also a common problem. All of the suggested methods are very nice but they will always point to a process, and there are many chances that we already know that our site is making problems, but we just want to know what specific page is spending too much time in processing. The most precise and simple tool in my opinion is IIS itself.

1. Just click on your server in the left pane of IIS.
2. Click on 'Worker Processes' in the main pane. you already see what application pool is taking too much CPU.
3. Double click on this line (eventually refresh by clicking 'Show All') to see what pages consume too much CPU time ('Time elapsed' column) in this pool

Answer 3

It's not much of an answer, but you might need to go old school and capture an image snapshot of the IIS process and debug it. You might also want to check out Tess Ferrandez's blog - she is a kick a** microsoft escalation engineer and her blog focuses on debugging windows ASP.NET, but the blog is relevant to windows debugging in general. If you select the ASP.NET tag (which is what I've linked to) then you'll see several items that are similar.