ETW Central

Over the last few years I’ve written over forty blog posts that discuss ETW/xperf profiling. I’ve done this because it’s one of the best profilers I’ve ever used, and it’s been woefully undersold and under documented by Microsoft. My goal has been to let people know about this tool, make it easier for developers and users to record ETW traces, and to make it as easy as possible for developers to analyze ETW traces.

Some of those posts have aged poorly, and the rest are hidden amongst the 210+ posts (really? wow) I’ve written. The purpose of this page is to be a central hub that links to the ETW/xperf posts that are still relevant. Also, I’ve updated many of the older posts to reflect changes in the ETW toolset (technically known as the Windows Performance Toolkit). For convenience this page is accessible as https://tinyurl.com/etwcentral.

The most important post describes how to record ETW traces. This is important because ETW traces can be recorded on one machine, and analyzed on another. This means that your customers or relatives can record ETW traces and then you can analyze them. Remote diagnosis of issues is a wonderful superpower. The article describing how to record an xperf/ETW trace can be found here – share it with those who have performance problems:

Xperf Basics: Recording a Trace (the ultimate easy way)

Once you’ve got a trace you need to analyze it (or share it with someone who can). The most comprehensive resource I’ve created for learning how to analyze ETW traces is the series of three videos I created in 2014. More information and links to the videos can be found here:

ETW Training Videos Available Now

For more details, or if you don’t want to watch videos, there are many tutorial blog posts available, listed here in rough order of importance:

• UIforETW – Windows Performance Made Easier
• WPA–Xperf Trace Analysis Reimagined – basics of WPA trace analysis
• Xperf for Excess CPU Consumption: WPA edition – basics of investigating CPU consumption
• Xperf Wait Analysis–Finding Idle Time – wait analysis (idle CPU investigations) with UIforETW and WPA 10
• New Xperf and new WPA in the new WPT – new features in WPT 10
• Graph All the Things (Using WPT 10) – graphing custom ETW data
• New Version of Xperf–Upgrade Now – new features in WPT 8.1
• ETW Heap Tracing–Every Allocation Recorded – tracing memory allocations
• ETW Heap Snapshots – tracing all outstanding allocations (much less data than ETW Heap Tracing)
• ETW Flame Graphs Made Easy – using WPA’s flame graphs to visualize CPU usage, and more
• Exporting Arbitrary Data from xperf ETL files
• CPU Performance Counters on Windows – recording per-process CPU performance counters using ETW
• Process Tree from an Xperf Trace – an example of exporting ETL data
• ETW Trace Compression (and xperf syntax refresher) – low-level details on how recording traces works, handy if you want to modify UIforETW
• Bulk ETW Trace Analysis in C#

Doing precise analysis of an ETW trace requires knowing exactly what the many columns in the tables mean. Some of those table columns are documented in these blog posts, updated in 2016 for the latest version of WPA:

• The Lost Xperf Documentation–CPU sampling
• The Lost Xperf Documentation—CPU Scheduling
• The Lost Xperf Documentation—Disk Usage

ETW investigation write-ups:

Some of my favorite blog posts are those that tell a tale of noticing some software that I use being slow, recording a trace, and figuring out the problem. In most cases this let me come up with a workaround, and in many cases the (ridiculously!) detailed bug reports or the attention the posts drew led to the problems being fixed.

Many of the articles linked to below have not yet been updated. It’s an ongoing process but I think it’s worth publishing this now without waiting for all of the updates to finish.

I’ve categorized the investigations by what product was investigated. And, as a reminder, with the exception of the fractal software investigation all of these are looking at problems in software that I don’t work on.

Visual Studio and VC++ code-gen:

• Xperf and Visual Studio: The Case of the Breakpoint Hangs
• Visual C++ Debug Builds–”Fast Checks” Cause 5x Slowdowns
• Visual Studio Single Step Performance Fixes
• Make VC++ Compiles Fast Through Parallel Compilation
• You Got Your Web Browser in my Compiler!
• Self Inflicted Denial of Service in Visual Studio Search
• 50 Bytes of Code That Took 4 GB to Compile

Windows Performance Toolkit (profiling the profiler!):

• Xperf Symbol Loading Pitfalls
• Slow Symbol Loading in Microsoft’s Profiler, Take Two
• Profiling the profiler: working around a six minute xperf hang

Windows:

• Delays in login to Windows due to thread rank – what outranks thread priority
• O(n^2), again, now in WMI
• Making VirtualAlloc Arbitrarily Slower – excessive CPU usage
• Hidden Costs of Memory Allocation – excessive CPU usage
• Taskbar Latency and Kernel Calls – excessive CPU usage (Windows bug)
  • Youtube video of this analysis is available here
• O(n^2) in CreateProcess – CFG causing problems again, excessive CPU usage (Windows bug, now fixed)
• A Not-Called Function Can Cause a 5X Slowdown – lock contention during process shutdown, caused by loading the wrong DLL (Windows quirk, triggered by llvm tests)
• Making Windows Slower Part 2: Process Creation – O(n^2) in CreateProcess due to Application Verifier
• 24-core CPU and I can’t type an email (part one) – lock contention during process shutdown (CFG, service workers, v8, WMI – it’s got everything, but it’s mostly Windows bugs)
• Making Windows Slower Part 1: File Access – slowing down Chrome builds with large notification buffers (Windows bug, now fixed)
• 24-core CPU and I can’t move my mouse – lock contention during process shutdown (Windows bug, now fixed)
• 63 Cores Blocked by Seven Instructions – NTFS lock contention bringing a build machine to its knees (Windows bug)
• Arranging Invisible Icons in Quadratic Time – this demonstrates how to use UI Delays to find where a hang is happening, CPU Usage (Precise) to prove that it’s a busy hand, and then CPU Usage (Sampled) to see where time is being spent. And then some surprisingly simple work to prove that it’s a quadratic algorithm.

Windows Live Photo Gallery:

• Windows Live Photo Gallery—Poor Performance Peculiarities (xperfview used for analysis, but concepts are still solid)
• Fixing another Photo Gallery performance bug

Western Digital driver (initially thought to be Windows):

• Windows Slowdown, Investigated and Identified

• Windows Slowdown, Investigated, Identified, and Now Fixed

Miscellaneous:

• Faster Fractals Through Better Scheduling
• PowerPoint Poor Performance Problem
• Defective Heat Sinks Causing Garbage Gaming

Other people’s ETW investigation write-ups:

• Interleaving small reads of multiple files – World of Tanks load times

Obsolete posts

Some of the blog posts are now completely obsolete and are listed here only for historical interest:

• Xperf Analysis Basics – obsolete or covered elsewhere
• Xperf Basics: Recording a Trace, replaced by Xperf Basics: Recording a Trace (the easy way) which was then replaced by Xperf Basics: Recording a Trace (the ultimate easy way) – third time’s the charm
• Xperf for Excess CPU Consumption – replaced by Xperf for Excess CPU Consumption: WPA edition
• The New Xperf is Here! – replaced by Xperf Basics: Recording a Trace (the ultimate easy way)
• The New WPA Xperf Trace Viewer–New Bugs and Old – the reported bugs are generally fixed
• Summarizing Xperf CPU Usage with Flame Graphs – WPA 10.0.14393 has built-in flame graphs which are covered here