How long should someone wait before he changes his fund?

I am doing a SIP for the last 1 year, and one of my funds is in giving negative returns from the last 6 months. How long should I keep investing in that mutual fund?

I understand that you need to keep patience in SIP, but there must be a point where you should start to think that okay this fund is not good for me and I need to get out of this before it is too late.