Before revision:  We further consider the problem under poisson arrival and general workload distribution,  M-SRPT is proved to be asymptotic optimal when the traffic intensity \rho approaches 1, if the task size is upper bound by the derived upper bound \eta{1-\rho}, if the job size distribution has bounded support, which generalizes the result in }[ .
After revision:  We further consider the problem under Poisson arrival and general workload distribution, M-SRPT is proved to be asymptotic optimal when the traffic intensity \rho approaches 1, if the task size is upper bound by the derived upper bound \eta{1-\rho}, if the job size distribution has bounded support, which generalizes the result in }[ .