Who wrote 3.15 through 3.17

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When writing up the 3.14 development statistics , your editor publicly wondered if compiling those reports for every development cycle made sense. That question was followed by a bit of a break; there were no "who wrote..." articles for the 3.15 or 3.16 development cycles. Now that just over six months have passed and the 3.17 kernel is nearing release, it seems like it may be time to take another look at how the kernel development process is working.

Since 3.14, kernel release activity has looked like this:

Version Date CSets Devs Lines (thousands) Added Removed Delta 3.15 Jun 8 13,722 1492 1066 707 360 3.16 Aug 3 12,804 1478 578 329 249 3.17 Sep 28* 12,153 1408 692 708 -16 3.15–17 38,679 2546 2336 1744 593

A few interesting things jump out of these numbers. The 3.12 cycle had contributions from 1257 developers. By 3.13, that had increased to 1339, and 3.14 had patches from exactly 1400 developers. So the count of developers contributing to each kernel release, which had hovered in the 1200's for some time, has shown a significant increase. The active kernel development community continues to grow.

The kernel itself also continues to grow, but 3.17 looks like a rare exception. Thanks to the removal of a bunch of unloved code from the staging tree, 3.17 is actually smaller than its predecessor. That has only happened one other time in the history of the Linux kernel; 2.6.36 was smaller than 2.6.35 thanks to the removal of a pile of defconfig files. The overall trend remains unchanged, though; the kernel grew by almost 600,000 lines in the last three releases.

As of 3.17-rc6, Linus was thinking that he would be able to do the 3.17 final release on September 28. Should that schedule hold, the 3.17 kernel will have been produced in a mere 56 days — as was 3.16. Your editor has remarked on the trend of the shortening kernel release cycle for a while. Here is what that trend looks like now (again, assuming the 3.17 release is not delayed):

So the kernel development cycle, it seems, continues to get shorter. How much longer that trend can continue is unclear, though; there must be a minimum period required to get a high-quality release together. One other potentially interesting point: it should be remembered that the final stabilization of the 3.15 release overlapped with the 3.16 merge window. That probably had little to do with why the 3.15 cycle took longer than many others; it was the result of some difficult-to-find last-minute bugs. But one could argue that the 3.16 development cycle should really be counted as being one week longer than the release dates would indicate.

Contributors

As can be seen from the table above, 38,679 non-merge changesets were pulled into the mainline repository for the 3.15–3.17 development cycles. Of the 2546 developers who contributed changes during this time, the most active were:

Most active developers, 3.15–3.17 By changesets Hartley Sweeten 919 2.4% Jes Sorensen 767 2.0% Malcolm Priestley 544 1.4% Fabian Frederick 382 1.0% Navin Patidar 378 1.0% Laurent Pinchart 330 0.9% Sachin Kamat 327 0.8% Russell King 316 0.8% Axel Lin 301 0.8% Johan Hedberg 300 0.8% Geert Uytterhoeven 296 0.8% Daniel Vetter 278 0.7% Takashi Iwai 275 0.7% Jingoo Han 265 0.7% Thomas Gleixner 260 0.7% Alexander Shiyan 240 0.6% Ville Syrjälä 235 0.6% Joe Perches 233 0.6% Tejun Heo 231 0.6% Lars-Peter Clausen 226 0.6% By changed lines Tomi Valkeinen 318894 10.9% Kristina Martšenko 165102 5.6% Larry Finger 164869 5.6% Andrzej Pietrasiewicz 108036 3.7% Mauro Carvalho Chehab 71253 2.4% Greg Kroah-Hartman 68260 2.3% Dave Chinner 48267 1.6% Devin Heitmueller 46125 1.6% Malcolm Priestley 35231 1.2% Jes Sorensen 29412 1.0% Navin Patidar 28871 1.0% Hans Verkuil 27813 0.9% Ben Skeggs 26293 0.9% Mark Hounschell 24285 0.8% Ken Cox 23213 0.8% Hartley Sweeten 21246 0.7% Jason Cooper 20344 0.7% Linus Walleij 19898 0.7% Jake Edge 18218 0.6% Maxime Ripard 14669 0.5%

As is usually the case, Hartley Sweeten contributed more changesets than any other developer; all of those were against the COMEDI drivers in the staging tree. All told, nearly 6,000 patches have been applied against just that subsystem since its entry into staging. Jes Sorensen's work was nearly all against the rtl8723au driver, while Malcolm Priestly worked on the vt6656 driver; both of those drivers are also in the staging tree. Fabian Frederick contributed cleanups throughout the kernel tree, while Navin Patidar focused on the rtl8188eu driver which, unsurprisingly, is also in the staging tree.

In the "lines changed" column, Tomi Valkeinen reached the top with extensive work on the ARM OMAP architecture code and related device tree files. Kristina Martšenko removed 14 drivers from the staging tree, making her the developer who removed the most code during this time. Larry Finger continues his work to rationalize the Realtek wireless drivers in the staging tree, Andrzej Pietrasiewicz did a lot of work in the USB gadget driver, and Video4Linux subsystem maintainer Mauro Carvalho Chehab did extensive work throughout that tree.

The 3.15–3.17 development cycles saw contributions from at least 312 employers, the most active of whom were:

Most active employers, 3.15–3.17 By changesets (None) 4492 11.6% Intel 4088 10.6% Red Hat 3577 9.2% (Unknown) 3409 8.8% Linaro 1702 4.4% Samsung 1646 4.3% SUSE 1243 3.2% IBM 1050 2.7% (Consultant) 1016 2.6% Texas Instruments 942 2.4% Vision Engraving Systems 919 2.4% Google 763 2.0% Renesas Electronics 753 1.9% Free Electrons 753 1.9% Freescale 620 1.6% C-DAC 400 1.0% Oracle 390 1.0% Imagination Technologies 361 0.9% NVidia 355 0.9% FOSS Outreach Program for Women 336 0.9% By lines changed (None) 408176 13.9% Texas Instruments 357058 12.2% (Unknown) 338760 11.6% Red Hat 259264 8.8% Samsung 249613 8.5% Intel 180869 6.2% Linaro 93125 3.2% Linux Foundation 68988 2.4% SUSE 52213 1.8% (Consultant) 45952 1.6% IBM 44809 1.5% Free Electrons 42917 1.5% Cisco 33254 1.1% Freescale 32636 1.1% C-DAC 30405 1.0% Renesas Electronics 29973 1.0% Google 29957 1.0% Realtek 27888 1.0% NVidia 27232 0.9% COMPRO Intelligent Solutions 24722 0.8%

As usual, this picture has remained relatively stable from one release to the next. Mildly notable is the increase in contributions from developers working on their own time, though it would be hard to say that the long-term trend toward decreasing volunteer contributions has ended at this point.

Reviews and conclusion

Finally, it can be interesting to look at who is attaching Reviewed-by tags to patches. That tag is meant both as an indicator that the patch has been reviewed and a means for crediting developers who perform those reviews. The developers with the most Reviewed-by tags during this period were:

Developers with the most Reviewed-by tags Ian Abbott 766 11.0% Josh Triplett 207 3.0% Tomasz Figa 155 2.2% Christoph Hellwig 142 2.0% Ville Syrjälä 132 1.9% Chris Wilson 123 1.8% Johannes Berg 122 1.8% Jesse Barnes 103 1.5% Guenter Roeck 98 1.4% Pieter-Paul Giesberts 92 1.3% David Herrmann 87 1.3% Dave Chinner 86 1.2% Hartley Sweeten 86 1.2% Imre Deak 84 1.2% Alex Elder 84 1.2% Rodrigo Vivi 80 1.2% Alex Deucher 74 1.1% Damien Lespiau 73 1.1% Daniel (Deognyoun) Kim 71 1.0% Franky (Zhenhui) Lin 66 1.0%

Ian Abbott, it seems, has reviewed 766 patches in the 182 days covered by these three development cycles — just over four patches every day, with no breaks for weekends or holidays. It turns out that almost all of those patches were the COMEDI changes submitted by Hartley Sweeten. Josh Triplett, instead, reviewed a wide range of changes from many developers; most of those were changes related to or involving read-copy-update. Tomasz Figa concerns himself with ARM-related changes, Christoph Hellwig is a longstanding reviewer of storage- and filesystem-related patches, and reviews changes to DRM (graphics) drivers.

What is not reflected here, of course, is the vast amount of patch review work that never results in a Reviewed-by tag. In fact, your editor would assert that this mechanism is not working as intended at this point. It is failing to document the bulk of the review work that is being done and serves mostly to highlight which developers make the effort to offer an explicit Reviewed-by tag.

To summarize: what has changed in the six months since LWN last published a set of development statistics? The answer is "not much." The kernel development process continues to roll along, producing releases in a fairly predictable schedule. The pace continues to increase, the community continues to grow, and the development cycle continues to shorten. These are all trends that we have seen for a while, so, to a great extent, it all looks like business as usual.

