Preemption time
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
These segments in the timeline are associated with the blocking time that is categorized as Pre-emption. This category implies that a thread is switched out because of one of these reasons:
The scheduler replaced it by using a higher priority thread.
The execution quantum of the thread expired and other threads were ready to execute.
During this time, a thread has been blocked by a kernel wait reason that the Concurrency Visualizer is counting as Pre-emption. Pre-emption segments start when a thread is pushed out of a logical core, and end when that thread resumes execution.
The tooltip for a pre-empted segment displays the name of the process or thread that caused the pre-emption. However, this does not imply that the process or thread that took over actually ran throughout the preempted period.