that is quite alot of oil.
But at the same time my mates dad has an audi a4 2ltr petrol. and that does about 800miles to a litre of oil.
Aslong as the exhaust is not smoking and no leaks on the floor, don't worry about it.
Just worry about the cost of the oil!

How many miles has it done?
If i were you maybe try giving a good full service, new oil, new oil filter, new sparks etc. See if clears anything out
Jake