Mathieu Desnoyers

Increasingly complex systems are being developed and put in production. Developers therefore face increas-ingly complex bugs. Kernel tracing provides an ef-fective way of understanding system behavior and de-bugging many types of problems in the kernel and in userspace applications. In some cases, tracing events that occur in application code can further help by pro-viding access to application activity unknown to the ker-nel. LTTng now provides a way of tracing simultaneously the kernel as well as the applications of a system. The kernel instrumentation and event collection facilities were ported to userspace. This paper describes the ar-chitecture of the new LTTng Userspace Tracer and how it can be used in combination with the kernel tracer. Results of some early performance tests are also pre-sented.