Longest delay was 115.6 ms on win32kbase.sys!EnterCrit, readied by conhost.exe (16264), thread 2560 at 3.273101862. Taskmgr.exe (72392) hung for 1.125 s (MsgCheckDelay) on thread 69,196. My notes from the analysis look something like this: I manually followed the wait chain through a half-dozen processes to see who was hogging the lock. The CPU Usage (Precise) table showed that Task Manager’s UI thread was repeatedly blocked on calls to functions like SendMessageW, apparently waiting on a kernel critical region (which are the kernel-mode version of critical sections), deep in the call stack in win32kbase.sys!EnterCrit (not shown): In the image below you can see CPU usage for the system during the hang, grouped by process name – notice that total CPU usage rarely goes above 50%: I decided to investigate a 1.125 s hang in Task Manager: The ETW trace showed UI hangs in multiple programs. The result was the discovery of a serious process-destruction performance bug in Windows 10. So I did what I always do – I grabbed an ETW trace and analyzed it. Maybe someday Microsoft will fix that, but probably not. That is, the mouse hitches and the horrible performance are still a risk. That issue was fixed but if many processes are destroyed that do have gdi32.dll loaded then the issue still happens. Update, September, 2020: the original issue was UserCrit contention while many processes were destroyed, whether they had gdi32.dll loaded or not. Update, August 17, 2018: analysis of an unrelated bug that also caused UI hangs due to lock contention is available here. Update, March 22, 2018: the fix has made it to Fall Creators Update (RS3), finally, so the fix is now everywhere. Update Nov 20, 2017: the fix has made it to Creators Update (RS2) which means I can now build Chrome without encountering micro-hangs! Update Oct 29, 2017: a video showing how to see if the bug is fixed can be found here, and the bug is fixed in the 17025 insider preview builds. Update July 27, 2017: a follow-up post dissects the problem and finds the root cause. And yet, as I moved the mouse around it kept hitching – sometimes locking up for seconds at a time. It has 64 GB of RAM and that was less than half used. My Windows 10 work machine has 24 cores (48 hyper-threads) and they were 50% idle. This story begins, as they so often do, when I noticed that my machine was behaving poorly.
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