Car consuming oil, leaving soot on ground

I have a 2010 Hyundai i30cw. It’s the FD, 2.0L Petrol Engine variant, Automatic Transmission.

Around five or six months ago I took it to the dealer for a service – they didn’t call out any issues, but since I got it back I’ve already had to refill the oil about four months after the service (their sticker doesn’t advise an oil change until 1 year has passed, or 10,000km and I’d only done about 5000km).

I also noticed that where I warm it up on my driveway, it has left a sooty black mark where the exhaust points down at the ground. It’s hard to say for sure, but perhaps the mileage has gotten very slightly worse (averaging 9.1L per KM where it used to be 8.9-9.0, however it’s possible my foot has been heavier in recent months).

The other day, I left the car idling for literally less than two minutes in a shopping centre car park while I was rearranging goods in the trunk and I saw that was enough time to deposit noticeable soot on the ground. The soot appears dry, not wet with water, and the exhaust otherwise looks normal, minimal, and white.

The car recently passed 300,000kms, I’ve owned it nearly a year and have put around 15,000kms on it in that time. Before the most recent service, it was not depositing soot.

Is this something I need to worry about and/or investigate further, or is it no big deal? The car otherwise performs just fine, no noticeable loss of power or performance.