1. A method of improving performance of a multi-subscriber-identification-module (multi-SIM) wireless communication device having at least a first SIM associated with a first radio-frequency (RF) resource and a second SIM associated with a second RF resource, wherein only the first RF resource is enabled to support operations on at least the first SIM, the method comprising: determining whether the first RF resource is in idle mode; and in response to determining that the first RF resource is in idle mode: identifying at least one idle-mode task to be performed by the first RF resource; identifying parallelism parameters that provide criteria to assist scheduling simultaneous idle-mode tasks; identifying possible parallelism task combination sets based on the at least one identified idle-mode task and the parallelism parameters; selecting a parallelism task combination set; and assigning at least one parallel task to each of the first and second RF resources according to the selected parallelism task combination set.