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

User · Answer

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    Just click on your server in the left pane of IIS   Click on  Worker Processes  in the main pane  you already see what application pool is taking too much CPU  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

User · Answer

This is a guess at best  but perhaps your development team is building and deploying the application in debug mode  in stead of release mode  This will cause the occurrence of  pdb files  The implication of this is that your application will take up additional resources to collect system state and debugging information during the execution of your system  causing more processor utilization   So  it would be simple enough to ensure that they are building and deploying in release mode

User · Answer

Also  look at your perfmon counters   They can tell you where a lot of that cpu time is being spent   Here s a link to the most common counters to use    http   www microsoft com technet prodtechnol WindowsServer2003 Library IIS 852720c8-7589-49c3-a9d1-73fdfc9126f0 mspx mfr true http   www microsoft com technet prodtechnol WindowsServer2003 Library IIS be425785-c1a4-432c-837c-a03345f3885e mspx mfr true

User · Answer

If you identify a page that takes time to load  use SharePoint s Developer Dashboard to see which component takes time

User · Answer

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

User · Answer

Standard Windows performance counters  look for other correlated activity  such as many GET requests  excessive network or disk I O  etc   you can read them from code as well as from perfmon  to trigger data collection if CPU use exceeds a threshold  for example  Custom performance counters  particularly to time for off-box requests and other calls where execution time is uncertain  Load testing  using tools such as Visual Studio Team Test or WCAT If you can test on or upgrade to IIS 7  you can configure Failed Request Tracing to generate a trace if requests take more a certain amount of time Use logparser to see which requests arrived at the time of the CPU spike Code reviews   walk-throughs  in particular  look for loops that may not terminate properly  such as if an error happens  as well as locks and potential threading issues  such as the use of statics  CPU and memory profiling  can be difficult on a production system  Process Explorer Windows Resource Monitor Detailed error logging Custom trace logging  including execution time details  perhaps conditional  based on the CPU-use perf counter  Are the errors happening when the AppPool recycles   If so  it could be a clue

User · Answer

Process nbsp Explorer is an excellent tool for troubleshooting  You can try it for finding the problem of high CPU usage  It gives you an insight into the way your application works   You can also try Procdump to dump the process and analyze what really happened on the CPU

User · Answer

We had this on a recursive query that was dumping tons of data to the output - have you double checked everything does exit and no infinite loops exist   Might try to narrow it down with a single page - we found ANTS to not be much help in that same case either - what we ended up doing was running the site hit a page watch the CPU - hit the next page watch CPU - very methodical and time consuming but if you cant find it with some code tracing you might be out of luck -   We were able to use IIS log files to track it to a set of pages that were suspect -   Hope that helps

User · Answer

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

[asp.net] W3WP.EXE using 100% CPU - where to start?

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