How to know I have done enough work in one semester? I am a PhD student in computer science (theory). I am worried about my productivity. I try to do as much as possible. I used to take four courses per semester during my first two years of studying. Now I have started doing research. In the last 4 months, I have only read 2-3 proofs and one research paper. It took 2-3 weeks to go over each mathematical proof. 

Question: How do I know I have done enough work in one semester? I mean is there any parameter to measure the work that I have done in the last semester? I have heard some students read only one research paper per one semester.

I can get feedback from my research supervisor, but the problem is he might say I did enough work just to keep my motivation high.
Everyone works at their own pace; moreover, the pace can fluctuate a lot depending on the time of year, your personal life, and "position of stars in the sky". Even though the semester seems like a decent amount of time to average out those fluctuations, I don't think it is.

I would try to use the following criteria to estimate the term success:


feedback from your advisor
how did the term go compared to the original plan (yep, here I assume that you make the plans for your term/month/week and correct them accordingly. Hopefully, some milestones are discussed with the advisor as well)
feedback from your committee (in some universities, Ph.D. students meet with their committee regularly or send them the progress report to hear their feedback)


I would certainly not recommend comparing your progress with other students because they are different, they have different goals, and you don't have complete information about their progress either. It is very easy to get discouraged for no reason.

To sum it up, I would stress the importance of initial planning and correcting the plans throughout the term. Then, you will have a very good measure of your success. You will end up with a different question of "how to plan", but that is a totally different problem.