Combined Tracing of the Kernel and Applications with LTTng

Increasingly complex systems are being developed and put in production. Developers therefore face increasingly complex bugs. Kernel tracing provides an effective way of understanding system behavior and debugging 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 providing access to application activity unknown to the kernel. 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 architecture 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 presented.