High CPU on w3wp

Question

I've deployed a .NET website to a 2008 (IIS7) server and the site seems to fly for up to 30-50 concurrent users. When load testing it the site comes to a grinding halt sometime after 100 concurrent users. Page loads go from 1.5 seconds to 90+

w3wp hits 100% and stays that way until I stop the load test. SQL on the other hand idles at about 2-3%.

I took a trace with debug diag and the report points to one of the threads that is taking up 11.358 cpu time vs 0.687 for the closest runner up. It's great that I've found the culprit, however I have no idea what to make of the info that I've been given. Here's the report output.

Thread 19 - System ID 4016 Entry point 0x00000000 Create time 7/8/2009 9:28:53 PM Time spent in user mode
0 Days 00:00:11.187 Time spent in kernel mode 0 Days 00:00:00.171

Function Source ntdll!KiFastSystemCallRet
ntdll!NtWaitForSingleObject+c
kernel32!WaitForSingleObjectEx+be
mscorwks!PEImage::LoadImage+1af
mscorwks!CLREvent::WaitEx+117
mscorwks!CLREvent::Wait+17
mscorwks!ThreadpoolMgr::SafeWait+73
mscorwks!ThreadpoolMgr::WorkerThreadStart+11c mscorwks!Thread::intermediateThreadProc+49 kernel32!BaseThreadInitThunk+e ntdll!__RtlUserThreadStart+23

ntdll!_RtlUserThreadStart+1b

Any help is appreciated!

Answer 1

I recommend you use a higher-level profiler. Here's a list:

• JetBrains' dotTrace
• Red-Gate ANTS
• Automated QA's AQTime

Answer 2

Check the performance monitor to see how many exceptions are being thrown, that uses a lot of cpu.