A fundamental problem that confronts SOA-based CSCW applications is the efficient and timely QoS information obtainment of component services. However, this issue has largely been overlooked. This paper presents a P2P based publish/subscribe service to disseminate new revised QoS information reliably and efficiently. Specialized rendezvous points and a replica mechanism are introduced to reduce the risk of subscriptions loss and consequently improve reliability. A message buffering and packaged delivery mechanism helps to reduce notification traffic. A reverse Chord ring, called RP ring, is designed to quicken subscription delivery and QoS information publication. Node partitioning technique is suggested to tackle the load balancing issue. Simulation results show that the service is reliable, efficient and scalable.