As users demand greater scalability from Citrix XenServer, the transmission of performance data from guests via xenstore is increasingly becoming a bottleneck. Future use of service domains is likely to make this problem worse. A simple, efficient way of transmitting time-varying datasets between userspace components in different domains is required. This talk will propose a lock-free mechanism to allow interdomain reporting of performance data without relying on continuous xenstore usage, and describe how it fits into the XAPI toolstack.