cregit: Who Authored the Kernel?

Recovering Token-Level Authorship Information from Git

Daniel M GermanUniversity of Victoria

dmg@uvic.ca

Kate StewartLinux Foundation

Bram AdamsPolytecnique of Montreal

Cincinnati LibraryImage in the public domain

diff-able

Image in the public domain

“History is writen by the winners”

By Y. Karsh. Image in the public domain in Canada. Copyrighted in the US

“Archeology is the search for fact, not truth. If it's truth you're interested in, Dr. Tyree's Philosophy class is right down the hall.”

-- Indiana Jones

Image Copyright Walt Disney Company

The history in git is likely to be incomplete

Yet, what can we do with it?

The Dream, by H. Rousseau. In the public domain.

Image in the public domain

Evolutionary Views of VC Repos

Per Line

Per Token

Linux History

Warning

● The author (git parlance) of a commit is not necessarily the author of the code

– Code imported from another source

– Refactorings

– Moving code

Up to 4.7

Persons in blame:

Line: 12,005 Token: 12,087

Token LineLinux

Token Line

kernel/

Many small changes

Non-merges that modified C and H files with respect to total of all commits

● 9.5 % of commits added 3 or less c-tokens and removed 3 or less c-tokens

● 7% of commits did not add any c-tokens but removed c-tokens

● 3.8% of commits added one c-token and removed one c-token

● 22.4% of commits added 10 or less c-tokens and removed 10 or less c-tokens

● 50% of commits added 60 or less c-tokens and removed 60 or less c-tokens

● 2 commits added at least 1M c-tokens and removed at least 1M c-tokens

C-Churn

● Churn = C Tokens added – C tokens removed in non-merge commits

Non-merges that modified C and H files with respect to total of all commits

● 10% of commits had c-churn == 0

● 48% had c-churn <= 10

● 26% had negative c-churn

● 2 commits had c-churn >= 1M

Conclusion

● On the large

– Token and Line areequivalent

● On the small

– Provide a fine grainedview of the evolutionof the code