The Linux kernel follows an extremely distributed reviewing and integration process supported by 130 developer mailing lists and a hierarchy of dozens of Git repositories for version control. Since not every patch can make it and of those that do, some patches require a lot more reviewing and integra- tion effort than others, developers, reviewers and integrators need support for estimating which patches are worthwhile to spend effort on and which ones do not stand a chance. This paper cross- links and analyzes eight years of patch reviews from the kernel mailing lists and committed patches from the Git repository to understand which patches are accepted and how long it takes those patches to get to the end user. We found that 33% of the patches makes it into a Linux release, and that most of them need 3 to 6 months for this. Furthermore, that patches developed by more experienced developers are more easily accepted and faster reviewed and integrated. Additionally, reviewing time is impacted by submission time, the number of affected subsystems by the patch and the number of requested reviewers.

1. Yujuan Jiang, Bram Adams (MCIS, Polytechnique Montréal)
Daniel M. German (University ofVictoria )
Will My Patch Make It?
And How Fast?
1
1Sunday, 19 May, 13

2. I do hold out hope that Google does
come around and works to fix their
codebase to get it merged upstream to
stop the huge blockage that they have
now caused in a large number of
embedded Linux hardware companies
[…] But I need the help of the Google
developers to make it happen, without
them, nothing can change.
http://www.kroah.com/log/linux/android-kernel-problems.html
2
Greg
Kroah-Hartman
2Sunday, 19 May, 13

3. Integration Process
3
3Sunday, 19 May, 13

4. Integration Process
3
Reviewing Integration Staging
3Sunday, 19 May, 13

5. Integration Process
3
Reviewing Integration Staging
3Sunday, 19 May, 13

6. Integration Process
3
contributor 1
contributor 2
contributor 3
Reviewing Integration Staging
3Sunday, 19 May, 13

7. Integration Process
3
contributor 1
contributor 2
contributor 3
Reviewing Integration Staging
3Sunday, 19 May, 13

8. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
Reviewing Integration Staging
3Sunday, 19 May, 13

9. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
Reviewing Integration Staging
3Sunday, 19 May, 13

10. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
Reviewing Integration Staging
3Sunday, 19 May, 13

11. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
Reviewing Integration Staging
3Sunday, 19 May, 13

12. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
subsystem
maintainer1
subsystem
maintainer1
Reviewing Integration Staging
3Sunday, 19 May, 13

13. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
subsystem
maintainer1
subsystem
maintainer1
Reviewing Integration Staging
3Sunday, 19 May, 13

14. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
subsystem
maintainer1
subsystem
maintainer1
Reviewing Integration Staging
3Sunday, 19 May, 13

15. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
subsystem
maintainer1
subsystem
maintainer1
Reviewing Integration Staging
3Sunday, 19 May, 13

16. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
subsystem
maintainer1
subsystem
maintainer1
Reviewing Integration Staging
maintainer
3Sunday, 19 May, 13

17. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
subsystem
maintainer1
subsystem
maintainer1
Reviewing Integration Staging
maintainer
3Sunday, 19 May, 13

18. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
subsystem
maintainer1
subsystem
maintainer1
Reviewing Integration Staging
maintainer Linus Torvalds
3Sunday, 19 May, 13

19. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
subsystem
maintainer1
subsystem
maintainer1
Reviewing Integration Staging
maintainer Linus Torvalds
3Sunday, 19 May, 13

20. Integration Process
3
contributor 1
contributor 2
contributor 3
linux-usb
linux-scsi
lkml
linux 3.5
subsystem
maintainer1
subsystem
maintainer1
Reviewing Integration Staging
maintainer Linus Torvalds
3Sunday, 19 May, 13

21. Research Questions
4
RQ1:
How many
patches are
merged?
RQ2:
What kind of
patch is merged
more likely?
RQ 3:
What kind of
patch is
accepted faster?
4Sunday, 19 May, 13

22. Setup Of Case Study
5
Reviewing Integration Staging
Linus Torvalds
linux-usb
linux-scsi
lkml
linux 3.5
contributor 1
contributor 2
contributor 3
subsystem
maintainer1
subsystem
maintainer1
maintainer
5Sunday, 19 May, 13

23. Setup Of Case Study
5
Reviewing Integration Staging
Linus Torvalds
linux-usb
linux-scsi
lkml
linux 3.5
contributor 1
contributor 2
contributor 3
subsystem
maintainer1
subsystem
maintainer1
maintainer
5Sunday, 19 May, 13

24. Setup Of Case Study
5
Reviewing Integration Staging
Linus Torvalds
linux-usb
linux-scsi
lkml
5Sunday, 19 May, 13

25. Setup Of Case Study
5
Reviewing Integration Staging
Linus Torvalds
linux-usb
linux-scsi
lkml
5Sunday, 19 May, 13

26. Setup Of Case Study
5
Reviewing Integration Staging
Linus Torvalds
5Sunday, 19 May, 13

27. Setup Of Case Study
5
Reviewing Integration Staging
Linus Torvalds
email1
email3
email2 email patch2
email patch1
email patch3
...
5Sunday, 19 May, 13

28. Setup Of Case Study
5
Reviewing Integration Staging
email1
email3
email2 email patch2
email patch1
email patch3
...
5Sunday, 19 May, 13

29. Setup Of Case Study
5
Reviewing Integration Staging
email1
email3
email2 email patch2
email patch1
email patch3
...
commit3
commit2
commit1commit patch1
commit patch2
commit patch3
...
5Sunday, 19 May, 13

30. Setup Of Case Study
5
Reviewing Integration Staging
email1
email3
email2 email patch2
email patch1
email patch3
...
commit3
commit2
commit1commit patch1
commit patch2
commit patch3
...
checksum1
checksum3
checksum2
...
5Sunday, 19 May, 13

31. Setup Of Case Study
5
Reviewing Integration Staging
email1
email3
email2 email patch2
email patch1
email patch3
...
commit3
commit2
commit1commit patch1
commit patch2
commit patch3
...
checksum1
checksum3
checksum2
...
5Sunday, 19 May, 13

32. Experience
Email
Review
E
Patch
Commit
6
5 Dimensions of
29 Patch Metrics
6Sunday, 19 May, 13

33. size: LOC > 50
Number of reviewers > 3 ?
not accepted Number of review messages > 3 ?
Is this first patch in thread?
not acceptedaccepted
Decision Tree
Building Decision Trees
7
7Sunday, 19 May, 13

34. 8
RQ1:
How many
patches are
merged?
RQ2:
What kind of
patch is merged
more likely?
RQ 3:
What kind of
patch is
accepted faster?
8Sunday, 19 May, 13

35. 9
RQ1:
How many
patches are
merged?
RQ2:
What kind of
patch is merged
more likely?
RQ 3:
What kind of
patch is
accepted faster?
9Sunday, 19 May, 13

36. RQ1:33% of patches make it!
10
2005 2006 2007 2008 2009 2010 2011 2012
accepted/rejected patches
percentageofpatches
0
20000
40000
60000
80000
100000
120000
28.63
28.7
27.03
32.83 32.79 33.87
33.55
30.74
71.37
71.3
72.97
67.17
67.21 66.13
66.45
69.26
% accepted by linus
% rejected by linus
#ofpatches
72.97%
67.17%
71.3%
71.73%
69.26%
66.45%
66.13%67.21%
28.63%
28.7%
32.79%
32.83%
27.03%
30.74%33.55%
33.87%
A
C
C
E
P
T
R
E
J
E
C
T
10Sunday, 19 May, 13

37. RQ1:Requiring 1~6months!
11
2005 2006 2007 2008 2009 2010 2011 2012
year
percentageofacceptedpatchesofeachyear
020406080
instantly
within_hour
within_day
within_week
within_month
within_quarter
within_half_year
within_year
took_ages
Text
%
accepted
patches
11Sunday, 19 May, 13

38. RQ1: reviewing time speeds up
& integration slows down
12
reviewing time integration time
12Sunday, 19 May, 13

39. 13
RQ1:
How many
patches are
merged?
RQ2:
What kind of
patch is merged
more likely?
RQ 3:
What kind of
patch is
accepted faster?
13Sunday, 19 May, 13

40. RQ2: What kind of patch is
merged more likely?
precision:73%
recall:68.47%
14
14Sunday, 19 May, 13

41. RQ2: What kind of patch is
merged more likely?
precision:73%
recall:68.47%
14
14Sunday, 19 May, 13

42. RQ2: What kind of patch is
merged more likely?
precision:73%
recall:68.47%
14
14Sunday, 19 May, 13

43. RQ2: What kind of patch is
merged more likely?
precision:73%
recall:68.47%
14
14Sunday, 19 May, 13

44. RQ2: What kind of patch is
merged more likely?
precision:73%
recall:68.47%
14
14Sunday, 19 May, 13

45. 15
RQ1:
How many
patches are
merged?
RQ2:
What kind of
patch is merged
more likely?
RQ 3:
What kind of
patch is
accepted faster?
15Sunday, 19 May, 13

46. RQ3: What kind of patch is
accepted faster?
16
16Sunday, 19 May, 13

47. RQ3: What kind of patch is
accepted faster?
16
16Sunday, 19 May, 13

48. RQ3: What kind of patch is
accepted faster?
16
16Sunday, 19 May, 13

49. RQ3: What kind of patch is
accepted faster?
16
16Sunday, 19 May, 13

50. RQ3: What kind of patch is
accepted faster?
16
16Sunday, 19 May, 13

51. RQ3: What kind of patch is
accepted faster?
16
16Sunday, 19 May, 13

52. RQ3: What kind of patch is
accepted faster?
16
Acceptance is
determined by
integration
phase
16Sunday, 19 May, 13

53. 17
17Sunday, 19 May, 13

54. 17
17Sunday, 19 May, 13

55. 2005 2006 2007 2008 2009 2010 2011 2012
year
percentageofpatches
0
20000
40000
60000
80000
100000
28.63
28.7
27.03
32.83 32.79 33.87
33.55
30.74
71.37
71.3
72.97
67.17
67.21 66.13
66.45% accepted by linus
% rejected by linus
72.97%
67.17%
71.3%
71.73%
66.45%
66.13%67.21%
28.63%
28.7%
32.79%
32.83%
27.03%
30.74%33.55%
33.87%
17
17Sunday, 19 May, 13

56. 2005 2006 2007 2008 2009 2010 2011 2012
year
percentageofpatches
0
20000
40000
60000
80000
100000
28.63
28.7
27.03
32.83 32.79 33.87
33.55
30.74
71.37
71.3
72.97
67.17
67.21 66.13
66.45% accepted by linus
% rejected by linus
72.97%
67.17%
71.3%
71.73%
66.45%
66.13%67.21%
28.63%
28.7%
32.79%
32.83%
27.03%
30.74%33.55%
33.87%
17
17Sunday, 19 May, 13

57. 2005 2006 2007 2008 2009 2010 2011 2012
year
percentageofpatches
0
20000
40000
60000
80000
100000
28.63
28.7
27.03
32.83 32.79 33.87
33.55
30.74
71.37
71.3
72.97
67.17
67.21 66.13
66.45% accepted by linus
% rejected by linus
72.97%
67.17%
71.3%
71.73%
66.45%
66.13%67.21%
28.63%
28.7%
32.79%
32.83%
27.03%
30.74%33.55%
33.87%
17
17Sunday, 19 May, 13