The ASM Service Time alarm is raised if the average time to retrieve data from an ASM (Automatic Storage Management) disk group appears excessive. High service times from the ASM disk group is normally caused by insufficient IO bandwidth within the group (too few disks, for example), or by a "hot disk" within the group.
Examine the ASM drilldown to determine if the service-time anomaly is isolated to a subset of disks. If it is, consider rebalancing the disk group. If ALL disks are showing poor service time, consider adding more disks to the disk group. Remember that the number of disks allocated to the disk group should be based on IO throughput requirements, not just storage space requirements.