Statistics from the 4.17 kernel development cycle
The 4.17 kernel, as of just after 4.17-rc7, has brought in 13,453 non-merge changesets from 1,696 developers. Of those developers, 256 made their first contribution to the kernel in this cycle; that is the smallest number of first-time developers since 4.8 (which had 237). The changeset count is nearly equal to 4.16 (which had 13,630), but the developer count is down from the 1,774 seen in the previous cycle.
Those developers added 690,000 lines of code, but removed 869,000, for a net reduction of nearly 180,000 lines. The main reason for the reduced line count, of course, is the removal of eight unused architectures. It's worth noting that, even with that much code hacked out, 4.17 will still be a little bit larger than 4.15.
The most active developers this time around were:
Most active 4.17 developers
By changesets Kuninori Morimoto 245 1.8% Kirill Tkhai 160 1.2% Arnd Bergmann 148 1.1% Chris Wilson 147 1.1% Colin Ian King 133 1.0% Alexandre Belloni 124 0.9% Rex Zhu 122 0.9% Dominik Brodowski 119 0.9% Christian König 119 0.9% Mauro Carvalho Chehab 106 0.8% Ajay Singh 102 0.8% Ville Syrjälä 100 0.7% Arnaldo Carvalho de Melo 99 0.7% Geert Uytterhoeven 94 0.7% Hans de Goede 86 0.6% Masahiro Yamada 83 0.6% Eric Dumazet 77 0.6% Gustavo A. R. Silva 72 0.5% Fabio Estevam 72 0.5% Linus Walleij 71 0.5%
By changed lines Arnd Bergmann 315103 22.9% Jesper Nilsson 100033 7.3% Greg Kroah-Hartman 81362 5.9% Feifei Xu 52509 3.8% David Howells 40705 3.0% Tom St Denis 32968 2.4% James Hogan 31998 2.3% Anirudh Venkataramanan 18937 1.4% Kuninori Morimoto 16175 1.2% Corentin Labbe 15265 1.1% John Crispin 13188 1.0% Yasunari Takiguchi 12983 0.9% Gilad Ben-Yossef 12426 0.9% Greentime Hu 11690 0.8% Rex Zhu 11458 0.8% Erik Schmauss 10980 0.8% Jacopo Mondi 10842 0.8% Harry Wentland 10198 0.7% Simon Horman 9179 0.7% Eric Biggers 8626 0.6%
Kuninori Morimoto contributed 245 patches, almost all concerned with a large renaming effort taking place in the ALSA sound driver subsystem. Kirill Thkai did a lot of work to increase parallelism in the network stack, Arnd Bergmann removed most of the old architecture code and did a lot of other cleanup (and year-2038) work throughout the kernel, Chris Wilson did a lot of work on the Intel i915 graphics driver, and Colin Ian King contributed a set of cleanup and typo-fixing patches.
The lines-changed column is dominated by Bergmann and Jesper Nilsson (who removed the Cris architecture). Greg Kroah-Hartman deleted a bunch of staging code (including the venerable IRDA infrared driver stack), Feifei Xu added more AMD GPU definitions, and David Howells removed the mn10300 architecture and did a bunch of filesystem-level work.
Work on 4.17 was supported by 241 companies that we were able to identify; the most active of those were:
Most active 4.17 employers
By changesets Intel 1392 10.3% (None) 977 7.3% Red Hat 870 6.5% (Unknown) 756 5.6% AMD 754 5.6% IBM 564 4.2% Renesas Electronics 559 4.2% Linaro 527 3.9% 448 3.3% Mellanox 405 3.0% SUSE 400 3.0% Bootlin 330 2.5% Samsung 268 2.0% Oracle 267 2.0% Huawei Technologies 244 1.8% Odin 232 1.7% ARM 222 1.7% (Consultant) 201 1.5% Canonical 188 1.4% Code Aurora Forum 181 1.3%
By lines changed Linaro 338103 24.6% AMD 138729 10.1% Axis Communications 100396 7.3% Intel 84613 6.2% Linux Foundation 81678 5.9% Red Hat 71152 5.2% Renesas Electronics 42565 3.1% (None) 35960 2.6% Imagination Technologies 32000 2.3% IBM 25841 1.9% ARM 23906 1.7% (Unknown) 22646 1.6% 21390 1.6% BayLibre 20931 1.5% Mellanox 19081 1.4% Bootlin 16256 1.2% (Consultant) 15353 1.1% Sony 14029 1.0% Fon 13188 1.0% Samsung 12823 0.9%
As usual, there are few surprises here.
The Reviewed-by tag was created to credit those who review code prior to its merging into the kernel. The actual use of that tag is sporadic at best, making it a poor guide to who is actually performing code review. But it still can be worth a look (and people complain when we don't post it). So here is a list of the top credited reviewers, alongside the counts of non-author signoffs (which are also an indicator of patch review):
Most active 4.17 code reviewers
Reviewed-by tags Alex Deucher 213 4.5% Rob Herring 192 4.1% Tony Cheng 123 2.6% Geert Uytterhoeven 108 2.3% Andrew Morton 102 2.2% Andy Shevchenko 94 2.0% Christian König 83 1.8% Chris Wilson 69 1.5% Daniel Vetter 64 1.4% Laurent Pinchart 57 1.2% Sebastian Reichel 56 1.2% Harry Wentland 56 1.2% Johannes Thumshirn 55 1.2% Hannes Reinecke 55 1.2% Christoph Hellwig 53 1.1% Guenter Roeck 51 1.1% Simon Horman 48 1.0% Darrick J. Wong 45 1.0% David Sterba 43 0.9% Ido Schimmel 42 0.9%
Non-author signoffs David S. Miller 1378 10.9% Greg Kroah-Hartman 876 7.0% Alex Deucher 640 5.1% Mark Brown 537 4.3% Mauro Carvalho Chehab 390 3.1% Andrew Morton 335 2.7% Ingo Molnar 318 2.5% Arnaldo Carvalho de Melo 213 1.7% Michael Ellerman 210 1.7% Herbert Xu 209 1.7% Jens Axboe 201 1.6% Martin K. Petersen 198 1.6% Kalle Valo 155 1.2% Thomas Gleixner 153 1.2% David Sterba 151 1.2% Jason Gunthorpe 134 1.1% Jeff Kirsher 133 1.1% Simon Horman 128 1.0% Doug Ledford 123 1.0% Shawn Guo 121 1.0%
Unlike many maintainers, Alex Deucher applies a Reviewed-by tag to many patches that he applies to his repository, causing him to show up in both columns. Rob Herring has reviewed a wide range of patches centered mostly around device-tree bindings and related issues; these patches were generally applied by somebody else. Geert Uytterhoeven reviews patches from a fair variety of authors, but he is not normally the maintainer who applies them.
Andrew Morton reviews far more code than he ever gets credit for. Until recently, though, that activity has not been reflected by Reviewed-by tags: he supplied exactly one in 2008, 14 in 2009, one in 2012, and one in 2015. That changed in January of this year when he started adding Reviewed-by tags to many of the patches he applies to his own tree; this is part of a broader effort to ensure that all memory-management patches are reviewed. Morton understands what it means to truly review a patch, so each of those tags certainly indicates a real amount of work.
Tony Cheng is an interesting and potentially different case. He is an employee of AMD and, seemingly without exception, his Reviewed-by tags are applied to patches from other AMD developers, and the reviews themselves do not appear on the public mailing lists. He also applies Reviewed-by tags to his own patches, which are relatively small and few in number (example). Reviewed-by tags from people working at the same company as the patch author are often looked at with suspicion by other developers, especially when the reviews happen behind closed doors. In truth, in-house reviews can be among the most rigorous and demanding — or they can be a rubber stamp. Either way, though, applying Reviewed-by tags to one's own patches is not how things are usually done.
The signoff column, of course, shows which maintainers have been accepting the most patches. It does not guarantee that the maintainer has reviewed all of those patches before applying them, though maintainers should ensure that somebody has reviewed them. In any case, there is certainly some amount of work implied by having signed off on a lot of patches.
Use of Reviewed-by tags would appear to be increasing; over time, that may help to bring the amount of review work in the kernel into clearer focus. For now, though, its use remains both spotty and inconsistent; it's better than no data at all, but it's not even close to a complete picture. Overall, these numbers, like all in this article, are far from perfect metrics about who is really doing the work to keep the kernel project going.
One thing that is clear from these numbers is that the kernel remains a
busy place — one of the busiest software-development projects on the
planet. It seems unlikely that things will slow down anytime soon.
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