In the consulting companies usually, you have a person who is collecting the feedback on you. It's called courier counselor, DGL, etc. Depending on your role it can be the Principal, Partner or Director who is collecting the feedbacks. The feedbacks are provided by the Managers and other partners you worked with according to certain criteria (different across the companies, but what matters is the overall score).
Every certain period of time there is an evaluation process when all the leadership of the office gets together and your case is presented. On these meetings, you get a certain performance rating (Can have different names but usually it's a performance scale). Then it's communicated to you directly.
All in all, if you are a top performer you have more flexibility in choosing the projects, faster career growth, get higher bonuses and relocation opportunities.