Development statistics for the 4.2 kernel

As of this writing, the 4.2-rc7 prepatch is out and the final 4.2 kernel looks to be (probably) on-track to be released on August 23. Tradition says that it's time for a look at the development statistics for this cycle. 4.2, in a couple of ways, looks a bit different from recent cycles, with some older patterns reasserting themselves.

At the end of the merge window, there was some speculation as to whether 4.2 would be the busiest development cycle yet. The current record holder is 3.15, which had 13,722 non-merge changesets at the time of its final release. 4.2, which had 13,555 at the -rc7 release, looks to fall a little short of that figure. So we will not have broken the record for the most changesets in any development cycle, but it was awfully close.

One record that did fall, though, is the number of developers contributing code to the kernel. The previous record holder (4.1, at 1,539) didn't keep that position for long; 1,569 developers have contributed to 4.2. Of those developers, 279 have made their first contribution to the Linux kernel. An eye-opening 1.09 million lines of code were added this time around with 285,000 removed, for a total growth of 800,000 lines of code.

The most active developers this time around were:

Most active 4.2 developers

By changesets Ingo Molnar 304 2.2% Mauro Carvalho Chehab 203 1.5% Herbert Xu 171 1.3% Krzysztof Kozlowski 161 1.2% Geert Uytterhoeven 149 1.1% Al Viro 140 1.0% Lars-Peter Clausen 137 1.0% H Hartley Sweeten 136 1.0% Thomas Gleixner 127 0.9% Hans Verkuil 124 0.9% Tejun Heo 110 0.8% Alex Deucher 95 0.7% Paul Gortmaker 91 0.7% Vineet Gupta 88 0.7% Jiang Liu 84 0.6% Christoph Hellwig 79 0.6% Hans de Goede 78 0.6% Arnaldo Carvalho de Melo 77 0.6% Mateusz Kulikowski 74 0.5% Takashi Iwai 73 0.5%

By changed lines Alex Deucher 425501 35.7% Johnny Kim 33726 2.8% Raghu Vatsavayi 14484 1.2% Greg Kroah-Hartman 12500 1.0% Stephen Boyd 11062 0.9% Dan Williams 10736 0.9% Hans Verkuil 10641 0.9% Narsimhulu Musini 10263 0.9% Ingo Molnar 9254 0.8% Jakub Kicinski 8531 0.7% Herbert Xu 8515 0.7% Yoshinori Sato 7612 0.6% Saeed Mahameed 7493 0.6% Sunil Goutham 7471 0.6% Christoph Hellwig 7384 0.6% Vineet Gupta 7171 0.6% Mateusz Kulikowski 6852 0.6% Maxime Ripard 6767 0.6% Sudeep Dutt 6647 0.6% Mauro Carvalho Chehab 6422 0.5%

Some years ago, Ingo Molnar routinely topped the per-changesets list, but he has been busy with other pursuits recently. That changed this time around, though, with a massive rewrite of the low-level x86 floating-point-unit management code. Mauro Carvalho Chehab continues to be an active maintainer of the media subsystem, and Herbert Xu's work almost entirely reflects his role as the maintainer of the kernel's crypto subsystem. Krzysztof Kozlowski contributed cleanups throughout the driver subsystem, and Geert Uytterhoeven, despite being the m68k architecture maintainer, did most of his work within the ARM tree and related driver subsystems.

On the "lines added" side, Alex Deucher accounted for nearly half of the entire growth of the kernel this time around with the addition of the new amdgpu graphics driver. Johnny Kim added the wilc1000 network driver to the staging tree, Raghu Vatsavayi added support for Cavium Liquidio Ethernet adapters, Greg Kroah-Hartman removed the obsolete i2o subsystem, and Stephen Boyd removed a bunch of old driver code while adding driver support for QCOM SPMI regulators and more.

The top contributor statistics in recent years have often been dominated by developers generating lots of cleanup patches or reworking staging drivers. One might expect to see a lot of that activity in an especially busy development cycle, but that is not the case for 4.2. Instead, the top contributors include many familiar names and core contributors. One might be tempted to think that the cleanup work is finally approaching completion, but one would be highly likely to be disappointed in future development cycles.

The most active companies supporting development in the 4.2 cycle (of 236 total) were:

Most active 4.2 employers

By changesets Intel 1665 12.3% Red Hat 1639 12.1% (Unknown) 884 6.5% (None) 884 6.5% Samsung 681 5.0% SUSE 496 3.7% Linaro 449 3.3% (Consultant) 412 3.0% IBM 391 2.9% AMD 286 2.1% Google 246 1.8% Renesas Electronics 203 1.5% Free Electrons 203 1.5% Texas Instruments 191 1.4% Facebook 176 1.3% Oracle 163 1.2% Freescale 156 1.2% ARM 145 1.1% Cisco 142 1.0% Broadcom 138 1.0%

By lines changed AMD 438094 36.8% Intel 96331 8.1% Red Hat 62959 5.3% (None) 46140 3.9% (Unknown) 41886 3.5% Atmel 34942 2.9% Samsung 29326 2.5% Linaro 22714 1.9% Cisco 21170 1.8% SUSE 18891 1.6% Code Aurora Forum 18435 1.5% Mellanox 18044 1.5% (Consultant) 15234 1.3% IBM 15095 1.3% Cavium Networks 14580 1.2% Free Electrons 13640 1.1% Unisys 13428 1.1% Linux Foundation 12617 1.1% MediaTek 11856 1.0% Google 11811 1.0%

Once again, there are few surprises here. At 6.5%, the percentage of changes coming from volunteers is at its lowest point ever. AMD, unsurprisingly, dominated the lines-changed column with the addition of the amdgpu driver. Beyond that, it is mostly the usual companies supporting kernel development in the usual way.

The kernel community depends heavily on its testers and bug reporters; at least some of the time, their contribution is recorded as Tested-by and Reported-by tags in the patches themselves. In the 4.2 development cycle, 946 Tested-by credits were placed in 729 patches, and 611 Reported-by credits were placed in 682 patches. The most active contributors in this area were:

Most active 4.2 testers and reporters
Tested-by credits Joerg Roedel 40 4.2% Keita Kobayashi 35 3.7% Krishneil Singh 31 3.3% Arnaldo Carvalho de Melo 30 3.2% Ira Weiny 24 2.5% Doug Ledford 23 2.4% Alex Ng 22 2.3% Aaron Brown 21 2.2% Javier Martinez Canillas 19 2.0% ZhenHua Li 19 2.0%	Reported-by credits Wu Fengguang 76 11.1% Dan Carpenter 41 6.0% Russell King 23 3.4% Ingo Molnar 12 1.8% Stephen Rothwell 10 1.5% Linus Torvalds 8 1.2% Hartmut Knaack 7 1.0% Huang Ying 6 0.9% Christoph Hellwig 5 0.7% Sudeep Holla 5 0.7%

The power of Wu Fengguang's zero-day build robot can be seen here; it resulted in 11% of all of the credited bug reports in this development cycle. The work of all of the kernel's testers and bug reporters leads to a more stable kernel release for everybody. The biggest concern with these numbers, perhaps, is that we might still not be doing a thorough job of documenting the contribution of all of our testers and reporters.

All told, the kernel development community continues to run like a well-tuned machine, producing stable kernel releases on a predictable (and fast) schedule. Back in 2010, your editor worried that the community might be headed toward another scalability crisis, but such worries have proved to be unfounded, for now at least. There must certainly be limits to the volume of change that can be managed by the current development model, but we do not appear to have reached them yet.

Index entries for this article
Kernel	Releases/4.2

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