Xen Developer & Design Summit 2018

The Xen domU create/destroy and device hotplug rely on xenwatch kernel thread to run xenwatch event callback function for each subscribed xenstore node update. Any event callback function hang would stall the only single xenwatch thread and forbid further domU create/destroy or device hotplug. This talk presents how Xenwatch Multithreading can address the xenwatch stall issue. In addition to the default xenwatch thread, the dom0 will create a per-domU kernel thread for each domU to handle their own xenwatch event. Therefore, domU create/destroy or device hotplug are still allowed even when a specific per-domU xenwatch thread is stalled. This talk first discusses the limitation in single-threaded xenwatch design with some case studies, then explains the basic knowledge on paravirtual driver, and finally presents the challenge, design and implementation of xenwatch multithreading.