The present invention relates to a multichip system and a method for scheduling threads in 3D stacked chip. The multichip system comprises a plurality of dies stacked vertically and electrically coupled together; each of the plurality of dies comprising one or more cores, each of the plurality of dies further comprising: at least one voltage violation sensing unit, the at least one voltage violation sensing unit being connected with the one or more cores of each die, the at least one voltage sensing unit being configured to independently sense voltage violation in each core of each die; and at least one frequency tuning unit, the at least one frequency tuning unit being configured to tune the frequency of each core of each die, the at least one frequency tuning unit being connected with the at least one voltage violation sensing unit. The multichip system and method described in present invention have many advantages, such as reducing voltage violation, mitigating voltage droop and saving power.