A look at the 4.14 development cycle

As of the 4.14-rc5 prepatch, 12,757 non-merge changesets had found their way into the mainline; that makes 4.14 slightly busier than its predecessor, but it remains a fairly normal development cycle overall. If, as some have worried, developers have pushed unready code into 4.14 so that it would be present in a long-term-support release, it doesn't show in the overall patch volume.

1,649 developers have contributed code in this development cycle, a number that will almost certainly increase slightly by the time the final 4.14 release is made. Again, that is up slightly from 4.13. Of those developers, 240 made their first contribution to the kernel in 4.14. The numbers are fairly normal, but a look at the most active developers this time around shows a couple of unusual aspects.

Most active 4.14 developers

By changesets Arvind Yadav 544 4.3% Bhumika Goyal 195 1.5% Gustavo A. R. Silva 156 1.2% Colin Ian King 151 1.2% Julia Lawall 141 1.1% Arnd Bergmann 127 1.0% Mauro Carvalho Chehab 117 0.9% Bart Van Assche 113 0.9% Arnaldo Carvalho de Melo 106 0.8% Paul Burton 100 0.8% Chris Wilson 96 0.8% Markus Elfring 94 0.7% Thomas Gleixner 87 0.7% Dan Carpenter 87 0.7% Laurent Pinchart 87 0.7% Daniel Vetter 83 0.7% Xin Long 82 0.6% Christoph Hellwig 79 0.6% Geert Uytterhoeven 77 0.6% Michael Ellerman 76 0.6%

By changed lines Greg Kroah-Hartman 129421 14.9% Ping-Ke Shih 122912 14.1% Lionel Landwerlin 30289 3.5% Mauro Carvalho Chehab 22461 2.6% Daniel Scheller 17708 2.0% Nick Terrell 14223 1.6% Aviad Krawczyk 12831 1.5% Salil Mehta 12051 1.4% Juergen Gross 11036 1.3% Todor Tomov 9286 1.1% Sukadev Bhattiprolu 9248 1.1% Hannes Reinecke 9003 1.0% Arnaldo Carvalho de Melo 7790 0.9% Andi Kleen 6826 0.8% Johannes Berg 6631 0.8% Masahiro Yamada 6429 0.7% Russell King 4573 0.5% John Fastabend 4412 0.5% Jérôme Glisse 4128 0.5% Vikas Shivappa 4091 0.5%

Arvind Yadav contributed 544 changesets mostly focused on making device-ID lists in the kernel constant. Unlike much "constification" work, these changes probably do not have much security significance, but they do tend to make the kernel text size a little smaller. Bhumika Goyal got her start as an Outreachy intern making structures full of function pointers const — a job that does improve security; she is continuing that work post-Outreachy with support from the Core Infrastructure Initiative (CII). Gustavo A. R. Silva also did constification work, along with contributing a number of other fixes, with CII support. Colin Ian King did, wait for it, constification work along with various other fixes and Julia Lawall also did constification work.

In other words, the top five contributors contributed nearly 1,200 changes mostly cleaning up declarations in the kernel. This work may not draw the same sort of attention as the addition of hardening mechanisms, but it is an important part of hardening the kernel overall.

Greg Kroah-Hartman got to the top of the "changed lines" column mostly by virtue of a single patch deleting the remaining old firmware files from the kernel tree. Firmware has long been maintained externally, so this cleanup was overdue. Ping-Ke Shih added yet another Realtek wireless driver to the staging tree, Lionel Landwerlin reworked parts of the Intel i915 driver in ways that allowed the removal of a lot of code, Mauro Carvalho Chehab contributed changes all over the media and documentation subsystems as usual, and Daniel Scheller added a large new media driver.

The 120,000-line Realtek wireless driver merits a bit more attention; it was the subject of some complaining about how Realtek gets its drivers into the kernel. But something of note has happened here. Numerous Realtek drivers have been merged via the staging tree, often moving on to the mainline kernel; that work has generally been done by Larry Finger on his own time. But, as he explained, he is reaching an age where he lacks the energy for this work and intends to stop soon. Thus it is encouraging that Ping-Ke Shih, the submitter of the Realtek driver patch this time around, is an actual Realtek employee. It would appear that the company has finally decided to put some resources into Linux support and, hopefully, the situation with its wireless drivers will improve over time. Meanwhile, Realtek should send Larry a nice retirement present — he has certainly earned it.

Work on 4.14 was supported by 213 companies that could be identified — a typical number that is, once again, a little higher than the 203 seen in the 4.13 cycle. The most active employers this time around were:

Most active 4.14 employers

By changesets Intel 1328 10.4% (None) 813 6.4% Red Hat 754 5.9% (Unknown) 575 4.5% IBM 566 4.4% Motorola 544 4.3% Linaro 500 3.9% Google 453 3.6% Mellanox 425 3.3% SUSE 404 3.2% Linux Foundation 391 3.1% AMD 348 2.7% Renesas Electronics 319 2.5% Samsung 262 2.1% Rockchip 257 2.0% Oracle 221 1.7% ARM 218 1.7% (Consultant) 199 1.6% Canonical 185 1.5% Broadcom 182 1.4%

By lines changed Linux Foundation 131369 15.1% Realtek 124976 14.4% Intel 101671 11.7% (None) 47222 5.4% Red Hat 31888 3.7% SUSE 29408 3.4% Huawei Technologies 28807 3.3% IBM 28363 3.3% Linaro 25614 2.9% Samsung 24940 2.9% (Unknown) 22749 2.6% Mellanox 18379 2.1% Facebook 18345 2.1% Google 17257 2.0% AMD 14621 1.7% (Consultant) 12162 1.4% Renesas Electronics 12004 1.4% ST Microelectronics 9923 1.1% Rockchip 9091 1.0% ARM 8438 1.0%

These results are fairly typical for recent kernels; the biggest surprise, perhaps, is the appearance of Realtek as was discussed above. In general, the kernel project continues to move forward powered by a great deal of corporate support.

While the kernel project clearly depends on developers to get the code written, it also depends on those who test changes and report bugs. Some of the time, at least, that contribution is noted through the addition of tags in the patches. Looking at the Reported-by (619 through 4.14-rc5) and Tested-by tags (605) yields the following results:

Testing and bug reporting in 4.14

Reported-by tags Fengguang Wu 36 5.8% Dan Carpenter 27 4.4% Andrey Konovalov 17 2.7% Peter Zijlstra 14 2.3% Eric Biggers 12 1.9% Arnd Bergmann 11 1.8% Michael Ellerman 11 1.8% Stephen Rothwell 9 1.5% kbuild test robot 7 1.1% Eric Dumazet 6 1.0% Dmitry Vyukov 6 1.0% Jianlin Shi 6 1.0% Christoph Hellwig 5 0.8% Geert Uytterhoeven 5 0.8% Ingo Molnar 5 0.8% Tetsuo Handa 5 0.8% kernel test robot 5 0.8% Mathias Kresin 5 0.8%

Tested-by tags Andrew Bowers 51 8.4% Richard Scobie 21 3.5% Arnaldo Carvalho de Melo 19 3.1% Laurent Pinchart 16 2.6% Thierry Reding 16 2.6% Andrey Konovalov 15 2.5% Laura Abbott 14 2.3% Eric Biggers 12 2.0% Jasmin Jessich 12 2.0% Dietmar Spingler 12 2.0% Manfred Knick 12 2.0% Aaron Brown 12 2.0% Marcin Wojtas 12 2.0% Pavel Machek 8 1.3% Philippe Cornu 7 1.2% Stan Johnson 7 1.2% Heiko Stuebner 6 1.0% Ondrej Zary 6 1.0%

In truth, the report credits for Fengguang Wu and the two "test robot" entries probably belong together, but they were credited separately in the patches.

These numbers, of course, greatly understate the amount of testing and reporting that is happening in the kernel community. The requisite tags do not always get added to patches as they should and, in the case of testing, many testers do not make themselves known in the first place if things work for them. That said, the tags that do exist record real work done, and the kernel is better for it.

Overall, the kernel development process would appear to continue to run relatively smoothly, despite the occasional hiccup. There are few projects that would be able to integrate changes at this rate and produce a result that will be the base for countless deployed systems in the coming years.