High CPU Usage with no load

1
votes

We are running a windows service which every 5 seconds checks a folder for files and if found logs some info about it using NLog.

I already tried the suggestions from ASP.NET: High CPU usage under no load without succes.

When the service was just started there is hardly any CPU usage. After a few hours we see CPU peaks to 100% and after some more waiting the cpu graph looks like:

windows task manager

I tried the steps described in http://blogs.technet.com/b/sooraj-sec/archive/2011/09/14/collecting-data-using-xperf-for-high-cpu-utilization-of-a-process.aspx to produce information on what is going on:

xperf overview

I don't know where to continue. Any help appreciated

2
performancewindows-servicescpu
That image is not very useful because it does not contain information how much time is spent where. All of this might be cold code. – usr
Actually I can't. It is just too much. That is why I was trying to use some tool to get info on what caused it – amaters

2 Answers

1
votes

Who wrote this windows service? Was it you or 3rd party?

To me, checking folder for changes every 5 seconds sounds really suspicious, and maybe the primary reason why you are getting this massive slowdown.

If you do it right, you can get directory changes immediately as they happen, and yet spend almost no CPU time while doing that.

This Microsoft article explains how exactly to do that: Obtaining Directory Change Notifications by using functions FindFirstChangeNotification, FindNextChangeNotification, ReadDirectoryChangesW and WaitForMultipleObjects.

1
votes

After a lot of digging it had to do with this:

The service had a private object X with property Y

Every time the service was fired X was passed to the Business Logic. There Y was used and in the end disposed. The garbage collector will then wait until X is disposed, which will never happen until the service is restarted. This caused an extra GC waiting thread every time the service was fired.