View the http redirect and response message from an external authentication provider using ETW


Recently I had to troubleshoot messages that were being sent from an web application hosted on IIS to an external authentication provider. The logs from the application wasn’t something closer to the metal and wasn’t really providing all the details. I really wanted something like fiddler for the webserver. I could have a ran network traces to troubleshoot the issue but the problem was it wasn’t happening consistently. It was sporadic. I knew there would be ETW traces that would have this information. The IIS web logs don’t capture this information.

Here is a example of the SAML authentication process

500px-SAML

In the application I was working with, IIS was the relying party and the user was to be authenticated with Identity Provider.

I wanted to troubleshoot the “AuthnRequest” and “Auth Resp” from and to the IIS. This can be applied to any external authentication like credit card authentication.

I fired my favorite tool Perfview and captured all the IIS traces along with other defaults. I wasn’t really interested in the .NET Code.

Here is the command line for Perfview to the IIS Providers

[gist https://gist.github.com/naveensrinivasan/86a6d7daac73484ef504]

If for some reason that does not work.  You could always use the additional providers in Perfview and add these providers which are IIS and HTTP providers.

[gist https://gist.github.com/naveensrinivasan/5ac34bdd047d2d80cc44]

I let perfview do its job and then stopped the trace when there was an issue.

Here are the ETW events that capture the SAML Request that was sent from IIS to the IDP

Event Name

  1. IIS_Trace/IISGeneral/GENERAL_RESPONSE_HEADERS
  2. Microsoft-Windows-IIS/EventID(47)
  3. IIS_Trace/IISGeneral/GENERAL_RESPONSE_ENTITY_BUFFER
  4. Microsoft-Windows-IIS/EventID(49)
  5. IIS_Trace/IISGeneral/GENERAL_REQUEST_HEADERS

SamlRequest

Here are the ETW events that capture the SAML Response that was being posted from the IDP to the IIS

  1. IIS_Trace/IISGeneral/GENERAL_REQUEST_ENTITY
  2. Microsoft-Windows-IIS/EventID(51)

samlresponse

With this I was able to troubleshoot message that was being sent and received to the IIS.

Use Eventsource to get the duration of a Start Stop of Custom ETW events


The EventSource library provides an option to get duration of Custom ETW start and stop events and when used with Perfview we could leverage this to stop tracing when the duration is more than what we expect.

What it is for example ,there could an external API call the application makes that has to be traced with the start and when it finishes then the stop of the event is called. Ideally we would have a ability to view the duration of these events similar to ASP.NET calls.  The EventSource Library along with Perfview provides this ability to view the duration between the start and stop events.

Here is a code sample with CustomEvent

[gist https://gist.github.com/naveensrinivasan/7e54c72dc628ae7da69e]

And here is the output from Perfview with the duration.

StartStopETW

How often we want to capture trace when the performance of our custom event goes down to figure out what went wrong. This is very much possible with this.

Here is the command

PerfView /StopOnEtwEvent:*CustomEvent//Start;TriggerMSec=2000 collect

This would record the ETW events on a flight recorder mode and would stop when the CustomEvent took more than 2 seconds. This is one of the features I really like because it is a great asset to DevOps to see when the issue arises.

Here is an example of Perfview Stop reason that shows why perfview stopped which clearly  indicates when the duration of event took more than 2000 milliseconds.

PerfviewStopReason

There is a bug in perfview that would not record Stop triggered events. I have reported this and I hope this would be fixed in the next public release.

The source code for these samples are here

https://github.com/naveensrinivasan/ETWSamples

Log dynamic Custom objects in ETW using EventSource


With the latest release of EventSource we could create dynamic events without having to create class that inherits from EventSource. This is will be not be good for Performance.

Using these methods we could either log Anonymous objects or Classes that have the EventData Attribute applied to it. The caveat is that these objects public properties alone will be serialized. These properties have to be of native types like string,int,datetime, guid , IEnumerable. If you don’t want a property to be serialized you could apply the attribute EventIgnore.

The source code for this repository is in https://github.com/naveensrinivasan/ETWSamples

Here is the sample code of using  Dynamic eventsource to generate ETW traces

[gist https://gist.github.com/naveensrinivasan/83ded09f7d754ad0b3a8]

Here is the trace from Perfview generated using

[gist https://gist.github.com/naveensrinivasan/11a793b35a18fc9546dd]

DynamicETW

The case of slow Visual Studio startup


In this post I would use Perfview /ETW to diagnose the delayed start-up of visual studio.

To analyze the problem start-up VS within Perfview as a run command

[gist https://gist.github.com/naveensrinivasan/5eb6406d6d38f2143acb]

This would launch visual studio and collect etw traces. I have also enabled CodeMarkers , which is ETW traces for Visual Studio in case if you want to trace any extensions performance.

perfview-mainAfter it completes I choose the CPU Stacks and filtered with devenv.exe process.

On the CPU window I choose call-tree tab which displays the threads.perfviewcpuviewThe most amount of time is spent on the start-up thread and that is what we want to zoom into.

groupedcall-stacksWhen I expanded it does not show the information and everything is grouped into OTHER which does not help me.

The reason for that is perfview groups call-stacks for better viewing. I cleared the “groupparts” textbox and then expanded the start-up thread.

actualcallstacksFrom the call-stacks I could make almost 42% of time is spent on Xamarin and DevExpress extensions within VS. Now I could turn them off and have a better performance.

Perfview is great tool for identifying where the time is being spent!

Measure GC Allocations and Collections using TraceEvent


In this post I will explore  how we could use TraceEvent to measure our code (even at function level) for GC Allocations and Collections.

Save this with “.linq” extension and then open in  linqpad.

Here is the TL;DR

Why would I want to know GC events on a function level? Doesn’t the PerfMon counter  provide that information on an application level? Isn’t Premature optimization root of all evil?

Yes, for most of the part Premature optimization is not necessary. And PerfMon GC counter’s would give answers for the whole application. But it is usually after we build the application and when we start running into performance issues we start looking at them.

The motivation behind this are two things Measure Early and Often for Performance and Essential Truths Everyone Should Know about Performance in a Large Managed Codebase

If you haven’t read or watched the above video please do it. It let’s us know why and how to do it.

In the above video Dustin talks about Roslyn code base and how they used Perfview to measure Roslyn code base and identify potential bottlenecks early to avoid Perf issues.

One of the key differences between managed code and native code with respect to performance is GC. If GC is working hard then your application might not be able to get the performance that you are expecting. GC is good but if we don’t know which calls allocate what amount of data then it is an issue. Especially if you have a section code that is hit very often and which requires a lot of Perf, it is good know where the allocations are coming from. It is not explicit always.

In the above video Dustin shows few examples of Roslyn code where they were able to identify subtle issues that could allocate a lot when you are trying to get the most out of the code.There is also Roslyn Heap Allocation Analyzer which looks at the code help us identify allocations which isn’t necessary. It is a cool project.

I took one of the examples from the video as a motivation to check if  I could measure and make it a utility in my toolbox to help me when I need one.

In the above example I am trying look for a word “pede” in the lorem ipsum text. The code could get it using “foreach” or using the “Any” operator. I would like to run this few times to check what are the allocations and how long does it take. I used LINQPad as a scratch pad.

Here is the result of GC Allocations of using “Any” for 500 iterations and NOT the foreach

GCAllocations

The were 118 allocations of Enumerator and 146 allocations Func. GC usually allocates 100K each time it allocates that’s what is shown in the allocation amount column.

And here is GC Allocations when using “foreach”

GCAllocationWithForEach

There are hardly any new allocations compared to the previous one.

Here is the GC Collections when using  “Any”

GCCollection

There were 18 GC Collections using Any.

Here it is using foreach  and there were 0 collections.

ZeorCollections

Here is measure it time duration results using Any

MeasureWithAny

And here it is using Foreach

MeasureWithForEach