val longList = 1 to 1000000 toList
val numsToAdd = sc.parallelize(longList,30)
val st = System.nanoTime()
println(numsToAdd.reduce((x,y) => x+y))
val et = System.nanoTime()
println("Time spend:"+(et-st))

Partitions     Time spend

 default        97916961

 10             111907094

 20             141691820

 30             158264230