Help required on Value Mapping

Dear All,

As i know there will be a communication between ID and IR at run time when value mapping is called.

We have to use the same value mapping for 30+ target fields and wanted to know whether Value mapping(IR and ID communication) will be called 30+ times or it will be called only once and its instance will be saved at run time and will use the same instance for other target fields.

if value mapping will be called for each target field mapping then it will reduce the performance?

Regards,

Manikandan