Where 4.3 came from

By Jonathan Corbet
October 27, 2015

As of the 4.3-rc7 release on October 25, the 4.3 development cycle appears to be headed for a conclusion on November 1, after the usual 63 days. It has been, by most appearances, an unremarkable development cycle, but it still saw the addition of a number of significant features; see the LWN merge window summaries (part 1, part 2, part 3) for details. It also included contributions from a record number of developers; read on for a look at where the code for 4.3 came from.

This development cycle has seen (so far) the inclusion of 12,131 non-merge changesets from an even 1,600 developers. The changeset count, while large, is far short of a record; it is also somewhat less than the 13,694 we saw for 4.2. This is the first cycle to hit 1,600 developers participating, though, beating 4.2's short-lived record of 1,591. The list of the most active developers includes some old names, along with a couple of new ones:

Most active 4.3 developers

By changesets

Ben Skeggs 266 2.2%

Viresh Kumar 167 1.4%

Thomas Gleixner 152 1.3%

Stephen Boyd 138 1.1%

Mateusz Kulikowski 138 1.1%

Geert Uytterhoeven 115 0.9%

Axel Lin 109 0.9%

Lars-Peter Clausen 103 0.8%

Thierry Reding 100 0.8%

Maarten Lankhorst 94 0.8%

Russell King 93 0.8%

H Hartley Sweeten 84 0.7%

Christian König 81 0.7%

Daniel Vetter 80 0.7%

Krzysztof Kozlowski 77 0.6%

Sudip Mukherjee 74 0.6%

Robert Baldyga 69 0.6%

Will Deacon 68 0.6%

Jiang Liu 67 0.6%

Javier Martinez Canillas 66 0.5%

By changed lines

Ben Skeggs 61416 7.6%

Mike Marciniszyn 57508 7.2%

Dennis Dalessandro 31557 3.9%

Jan Kara 29151 3.6%

Doug Ledford 14067 1.8%

Sinclair Yeh 12518 1.6%

Adrian Hunter 12513 1.6%

David Zhang 10149 1.3%

Alex Deucher 9970 1.2%

Thomas Hellstrom 9963 1.2%

Masahiro Yamada 9830 1.2%

Christian Gromm 9716 1.2%

Steve Wise 9158 1.1%

Matthew R. Ochs 7657 1.0%

Geert Uytterhoeven 7338 0.9%

Thierry Reding 7321 0.9%

Jason A. Donenfeld 6592 0.8%

Kozlov Sergey 6266 0.8%

Herbert Xu 6246 0.8%

Jiri Pirko 6166 0.8%

Ben Skeggs works with the Nouveau driver; this time around, he ended up at the top of both lists as the result of this work. The Nouveau tree missed the 4.2 merge window, so there are two cycles worth of patches showing up in 4.3. Other top changeset contributors include Viresh Kumar (mostly work adapting code to a new clockevents interface), Thomas Gleixner (changes to the interrupt-handling subsystem and fallout throughout the driver tree), Stephen Boyd (various driver-oriented patches, including some clock API changes), and Mateusz Kulikowski (cleanups to the rtl8192e driver in the staging tree).

Below Ben in the "lines changed" column are Mike Marciniszyn (added the "hfil" InfiniBand driver, containing work by numerous authors), Dennis Dalessandro (moved the "ipath" InfiniBand driver to the staging tree in preparation for its eventual removal), Jan Kara (removal of the ext3 filesystem), and Doug Ledford (moved the "ehca" InfiniBand driver to staging in preparation for its eventual removal).

The removal of code thus played a significant part of this development cycle. Even so, the net result of this cycle's patches was an addition of 382,000 lines to the kernel.

Just under 200 employers (that we know of) supported work on the 4.3 kernels; the most active of those were:

Most active 4.3 employers

By changesets

Intel 1590 13.1%

Red Hat 1139 9.4%

(Unknown) 956 7.9%

(None) 704 5.8%

Samsung 634 5.2%

Linaro 477 3.9%

IBM 343 2.8%

SUSE 294 2.4%

(Consultant) 284 2.3%

Texas Instruments 277 2.3%

AMD 265 2.2%

Freescale 249 2.1%

ARM 220 1.8%

Code Aurora Forum 218 1.8%

Google 206 1.7%

Mellanox 171 1.4%

Renesas Electronics 166 1.4%

Oracle 144 1.2%

NVidia 143 1.2%

Facebook 133 1.1%

By lines changed

Intel 178120 22.2%

Red Hat 117739 14.7%

SUSE 39218 4.9%

(Unknown) 37150 4.6%

AMD 31286 3.9%

(None) 24263 3.0%

VMWare 23031 2.9%

Linaro 22211 2.8%

IBM 18854 2.3%

Samsung 17325 2.2%

Mellanox 17100 2.1%

Microchip Technology 14595 1.8%

(Consultant) 12889 1.6%

NVidia 11452 1.4%

Renesas Electronics 11426 1.4%

Freescale 11419 1.4%

Socionext Inc. 9875 1.2%

Open Grid Computing 9181 1.1%

Texas Instruments 8953 1.1%

ARM 8570 1.1%

This table looks much like it has in recent cycles. The percentage of changes from volunteers continues its long-term slide; the 5.8% seen here is the lowest ever.

We may be getting fewer volunteer developers, but there are still plenty of developers entering the kernel community: 284 developers made their first kernel patch during the 4.3 development cycle. That is the most new developers for any development cycle ever — with one exception: 332 developers made their first patch to 2.6.25 in 2008. Of those 284 developers, 152 are already known to be working for a company; many of the remaining 132 will turn out to be employed as well. So starting as a volunteer is clearly not the path into the kernel community for most developers.

Intel employs 22 of those new developers, Samsung employs eight, and IBM seven; no other company employed more than six new developers. The most popular place for new developers to start was the staging tree (56 developers made changes there), followed by drivers/net (23), and arch/arm (21). The rest of the first changes were spread all over the tree, though most of them touched something in the driver subtree.

All told, the community continues to look healthy. There are more developers working on the kernel than ever before, and they are being introduced into the community by a wide variety of companies, many of which appear to be paying them to learn how to be kernel developers. The companies working in this area have clearly learned that they need to develop talent in-house to be able to participate in the process. That suggests that we will continue to have new developers showing up as long as Linux remains strong — an outcome that all those new developers will help assure.

Index entries for this article
Kernel	Releases/4.3