Efficient usage of shared high-performance computing (HPC) resources raises the problem of HPC applications co-scheduling, i.e. the problem of execution of multiple applications simultaneously on the same shared computing nodes. Each application may have different requirements for shared resources (e.g. network bandwidth or memory bus bandwidth). When these resources are used concurrently, their resource throughputs may decrease, which leads to performance degradation. In this paper we define application behavior model in co-scheduling environment and formalize a scheduling problem. Within the model we evaluate trivial strategies and compare them with an optimal strategy. The comparison provides a simple analytical criteria for choosing between a naive strategy of running all applications in parallel or any sophisticated strategies that account for applications performance degradation.