Among other things, this document describes systems, methods and devices for performance testing and dynamic placement of computing tasks in a distributed computing environment. In embodiments, a given client request is forwarded up a hierarchy of nodes, or across tiers in the hierarchy. A particular computing node in the system self-determines to perform a computing task to generate (or help generate) particular content for a response to the client. The computing node injects its identifier into the response indicating that it performed those tasks; the identifier is transmitted to the client with particular content. The client runs code that assesses the performance of the system from the client's perspective, e.g., in servicing the request, and beacons this performance data, along with the aforementioned identifier, to a system intelligence component. The performance information may be used to dynamically place and improve the placement of the computing task(s).