My environment: Windows Server 2008, IIE 7.0, ASP.NET
I developed a Silverlight client. This client gets updates from the ASP.NET host through a WCF web service.
We get 100% CPU usage and connection drops when we have a very low number of users (~50). The server should clearly be able to handle a lot more than that.
I ran some tests on our DEV server and indeed 100 requests / s maxes out the CPU. What's odd is that even if the service is replaced by a dummy sending back hardcoded data the service still maxes out the CPU. The thread count looked very low at about 20 so I thought there was some contention somewhere.
I changed all configuration options I could find to increase the worker threads (processModel, httpRuntime and the MaxRequestsPerCPU registry entry).
Nothing changed.
Then I stopped the IIS server and ran the web service as a console (removing all the ASP authentication references). The service maxed out the CPU as well.
Then comes the magic part: I killed the console app and restarted IIS and now the service runs a 5-60% CPU with 100 requests / s and I can see 50+ worker threads. I did the same thing on our preprod machine and had the same magic effect. Rebooting the machines keeps the good behaviour.
So my question is: what happened to fix my IIS server? I really can't understand what fixed it.
Cheers.
Find out the root cause of the high CPU usage, and then you can find a fix,