Should the food commodities be consumed or traded for generating biofuel?When will such conflict start?

I think that it's  already started. Look at the price of corn and other grain crops used for Bio-fuels. Because of the subsidies on offer, these fuel crops are starting to replace food crops.
What can be done to avoid a worldwide crisis in foodsupply? Stop growing fuel crops. Bio-Fuel is not the answer to the (soon) declining oil supply and the rising oil demand (3.5% a year). Bio-Fuel is like a sticking plaster on an open wound. It's being helped along by oil companies who want the world to use as much oil as possible for as long as possible while (allegedly) doing all they can to stop R&D into viable alternatives. Bio-Fuel is not a viable alternative due to the amount of fertilisers used in temperate climates, and the amount of deforestation in tropical climates.

But if I see and understand your questons in broader prespective, three things need to be focussed. Suppliers of commodities which can either be made into fuel or consumed.

But currently the  only commodity today of which I am most aware that could do both is corn. But there are problems with this model because today it is (supposedly) too expensive to convert corn to fuel when compared to just using oil. While I'm not sure of the reasons, if it's because the corn is too expense, then no conflict will occur until the price of corn goes down. But if the price of corn goes down, then that would be a good thing for consumers of corn. So, I don't see a conflict developing.

As someone else pointed out, making fuel from bio-mass might also help. The problem with that scenario (today) is that the right enzymes don't exist and other methods for breaking down cell walls is too expensive. I understand that top scientists believe that they are only a few years away from a break-through, so keep your fingers crossed. (I have heard stories of larger corporations stockpiling bio-mass with the idea that they will eventually be able to convert these piles to fuel).