iis, Need help with 'possible' Context Switch Issue - on IIS6

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iis >> Need help with 'possible' Context Switch Issue - on IIS6

by livin » Thu, 10 Nov 2005 04:45:43 GMT

I'm new to IIS (but very enterprise windows experienced) so please bear with
me...

Situation:
(4) IIS6 servers using WLBS
- running the same set of web sites (6 virtual sites per)
- same core code behind each site (only chages are the images - I know
there are better ways but I did not create the sites)

Using PerfMon (see info on 1 server below) I found that the context switches
jump direcly inline with the CPU hitting 100%...
this occurs constantly. I logged on 7 second intervals.

I logged all the IIS related process threads and it looks like all the
threads have the problem, different ones at different times, no noticable
pattern.

How can I isolate what process is causing the problem?

I was thinking of taking several IISstate logs but what should I focus it
on? I've never used IISstate, how do I know what processes to target?

Thank you in advance for the help!!!

info from one server:

CPU utilization
- spikes to 100% on a regular intervals, ave is under 2%
- this corresponds with user and kernel activity spiking at the same exact
times.
Pages per Second
- spikes to over 450 quite often, average is approx 1
Disk transfers/sec
- ave is 6 but it often spikes much higher and up to 125.
DPC (Deferred procedure calls)
- corresponding to CPU being maxed at the same times DPC occurs
Context Switches
- spikes on regular intervals, min is 194, ave is 276 and max up to 6524.
Processor Queue Length
- jumps from 0 to 30.





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iis >> Need help with 'possible' Context Switch Issue - on IIS6

by David Wang [Msft] » Thu, 10 Nov 2005 05:19:53 GMT


Since you are running the same core code behind each site, I would start by
assuming that the context switch is triggered by something within the user
code that you are running on each site. Hence it reproduces itself across
various w3wp.exe because the same code is running and just images are
changed.

You will need to identify what sort of code is running on these websites
(CGI, ISAPI, ASP, ASP.Net, Perl, PHP, JSP, etc) because that may affect the
analysis options available.

Debuggers like IIS State is unlikely to help with the sort of analysis you
want to do. I know what tool we use to identify and analyze code doing
context switches, but I do not know if you have that tool or not. Doing a
quick search of microsoft.com shows that the tool is mentioned a few times
but not available for download.

FYI:
I know that from your perspective, you can only identify that there are
context switch issues and it looks to be within IIS processes -- hence you
say "possible" contexts witch issue on IIS6 -- but from my perspective, this
is most likely performance issues within user code running on the website so
it is really not an IIS issue. You just need to be able to point the finger
back at the site developers to fix their code.

--
//David
IIS
http://blogs.msdn.com/David.Wang
This posting is provided "AS IS" with no warranties, and confers no rights.
//

I'm new to IIS (but very enterprise windows experienced) so please bear with
me...

Situation:
(4) IIS6 servers using WLBS
- running the same set of web sites (6 virtual sites per)
- same core code behind each site (only chages are the images - I know
there are better ways but I did not create the sites)

Using PerfMon (see info on 1 server below) I found that the context switches
jump direcly inline with the CPU hitting 100%...
this occurs constantly. I logged on 7 second intervals.

I logged all the IIS related process threads and it looks like all the
threads have the problem, different ones at different times, no noticable
pattern.

How can I isolate what process is causing the problem?

I was thinking of taking several IISstate logs but what should I focus it
on? I've never used IISstate, how do I know what processes to target?

Thank you in advance for the help!!!

info from one server:

CPU utilization
- spikes to 100% on a regular intervals, ave is under 2%
- this corresponds with user and kernel activity spiking at the same exact
times.
Pages per Second
- spikes to over 450 quite often, average is approx 1
Disk transfers/sec
- ave is 6 but it often spikes much higher and up to 125.
DPC (Deferred procedure calls)
- corresponding to CPU being maxed at the same times DPC occurs
Context Switches
- spikes on regular intervals, min is 194, ave is 276 and max up to 6524.
Processor Queue Length
- jumps from 0 to 30.
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set of four servers (using WLBS) running the same set of web sites (about 6
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While doing some baselining (using perfmon) I found that the context
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