Statistics from the 5.2 kernel — and before

1,716 developers contributed changes for the 5.2 kernel, 245 of whom made their first contribution during this cycle. Those 1,716 developers removed nearly 490,000 lines of code, which is a lot, but the addition of 596,000 new lines of code means that the kernel still grew by 106,000 lines. The most active developers this time around were:

Most active 5.2 developers

By changesets Thomas Gleixner 441 3.2% Alexandre Belloni 186 1.4% Yue Haibing 171 1.3% Chris Wilson 168 1.2% Guenter Roeck 160 1.2% Ville Syrjälä 135 1.0% Christoph Hellwig 125 0.9% Axel Lin 110 0.8% David Sterba 107 0.8% Christophe Leroy 106 0.8% Gustavo A. R. Silva 104 0.8% Colin Ian King 101 0.7% Bart Van Assche 99 0.7% Alex Shi 96 0.7% Masahiro Yamada 93 0.7% David Ahern 88 0.6% Maxime Ripard 88 0.6% Andy Shevchenko 83 0.6% Arnd Bergmann 79 0.6% Laurent Pinchart 78 0.6%

By changed lines Greg Kroah-Hartman 132179 14.4% Thomas Gleixner 126547 13.8% Yan-Hsuan Chuang 47518 5.2% Gabriel Krisman Bertazi 20170 2.2% Liam Girdwood 17379 1.9% Olaf Weber 13441 1.5% Andi Kleen 12232 1.3% Hans Verkuil 11709 1.3% Chris Wilson 10025 1.1% Mauro Carvalho Chehab 9809 1.1% Vladimir Oltean 7074 0.8% Gal Pressman 6143 0.7% David Howells 5652 0.6% Neil Brown 5345 0.6% Linus Walleij 5023 0.5% Rob Herring 5023 0.5% Tzvetomir Stoyanov 4998 0.5% Ryder Lee 4890 0.5% Tony Lindgren 4868 0.5% Neil Armstrong 4783 0.5%

Of the 441 patches that put Thomas Gleixner at the top of the "by changesets" column, 349 were a part of the ongoing effort to add SPDX tags to every kernel source file. That still leaves nearly 100 changes for little issues like the the microarchitectural data sampling vulnerabilities, reworking the handling of stack traces, and more. Alexandre Belloni contributed a long list of realtime clock changes, Yue Haibing made code cleanups all over the tree, Chris Wilson made many changes to the i915 graphics driver, and Guenter Roeck made a lot of improvements to the hardware monitoring and watchdog subsystems.

In the "lines changed" column, Greg Kroah-Hartman deleted the rtlwifi driver from the staging tree; it has been superseded by a non-staging driver. One might not think that adding a single SPDX line to files would lead to a lot of changed lines, even when a lot of files are involved, but most of those additions also allowed the removal of a lot of license boilerplate. As a result, Gleixner's SPDX work resulted in the removal of over 100,000 lines from the kernel. Yan-Hsuan Chuang only contributed three changes, but they brought in the new production Realtek driver, which is not small. Gabriel Krisman Bertazi added support for case-insensitive file-name lookups to the ext4 filesystem; that, in turn, brought in a large body of automatically-generated code for UTF-8 handling. Liam Girdwood add the Sound Open Firmware system.

The top testers and reviewers this time around are a bit different from the usual crowd:

Test and review credits in 5.2

Tested-by Andrew Bowers 132 16.6% Sebastian Reichel 45 5.7% Zhang Lei 24 3.0% Leo Yan 20 2.5% Robert Walker 20 2.5% Arnaldo Carvalho de Melo 14 1.8% Jon Hunter 13 1.6% Jon Masters 12 1.5% Jerome Brunet 11 1.4% Brice Goglin 10 1.3% Stefan Wahren 10 1.3% Aaron Brown 10 1.3% Mathieu Malaterre 9 1.1% Holger Hoffstätte 9 1.1% Bart Van Assche 8 1.0% Jeffrey Hugo 8 1.0% Oleksandr Natalenko 8 1.0% Sudip Mukherjee 8 1.0% James Smart 7 0.9% Michał Mirosław 7 0.9% Robert Yang 7 0.9%

Reviewed-by Allison Randal 345 5.4% Rob Herring 199 3.1% Kate Stewart 174 2.7% Richard Fontana 157 2.4% Alexios Zavras 120 1.9% Mukesh Ojha 116 1.8% Huang Rui 107 1.7% David Sterba 103 1.6% Alex Deucher 100 1.6% Tvrtko Ursulin 99 1.5% Armijn Hemel 96 1.5% Florian Fainelli 85 1.3% Simon Horman 79 1.2% Andrew Lunn 77 1.2% Takashi Iwai 74 1.2% Chris Wilson 73 1.1% Steve Winslow 65 1.0% Guenter Roeck 63 1.0% Christoph Hellwig 62 1.0% Mauro Carvalho Chehab 60 0.9%

Andrew Bowers apparently tested a large number of i40e network-driver patches written by co-workers at Intel. Then, there are some familiar names in the review column. People like Allison Randal, Kate Stewart, and Richard Fontana are all quite well known in our community, but they tend not to show up often in kernel patches. In this case, all of them spent time (along with Alexios Zavras and Armijn Hemel) reviewing the SPDX changes. This is important work: the addition of SPDX lines must reflect the actual license of each file and not inadvertently change that license.

Work on 5.2 was supported by 215 employers (that we know of), the most active of which were:

Most active 5.2 employers

By changesets Intel 1684 12.4% (Unknown) 1063 7.8% Red Hat 859 6.3% Google 730 5.4% (None) 633 4.7% AMD 544 4.0% Linutronix 480 3.5% SUSE 423 3.1% IBM 411 3.0% Linaro 370 2.7% Huawei Technologies 367 2.7% Bootlin 360 2.6% Mellanox 354 2.6% ARM 305 2.2% (Consultant) 295 2.2% Renesas Electronics 276 2.0% Oracle 217 1.6% NXP Semiconductors 182 1.3% Linux Foundation 160 1.2% BayLibre 159 1.2%

By lines changed Linux Foundation 132863 14.5% Linutronix 127352 13.9% Intel 99721 10.9% Realtek 47705 5.2% (Unknown) 35515 3.9% Red Hat 34869 3.8% AMD 23993 2.6% Collabora Multimedia 22794 2.5% Linaro 22696 2.5% Google 22450 2.5% (None) 22200 2.4% IBM 19651 2.1% MediaTek 14937 1.6% Mellanox 14657 1.6% Cisco 14656 1.6% Samsung 14260 1.6% SUSE 13559 1.5% SGI 13441 1.5% ARM 12407 1.4% BayLibre 11753 1.3%

There are few surprises here, as usual. It is nice to see Realtek showing up as a top contributor, though — a change from the recent past.

When developers apply a Signed-off-by tag to a patch that they did not write, it is usually an indication that they are merging that patch into a subsystem tree. A look at non-author signoffs thus gives an idea of who the gatekeepers for the kernel are. In 5.2, the most active developers in this role, and the companies that supported them, are:

Most non-author signoffs

Individuals David S. Miller 1214 9.4% Greg Kroah-Hartman 1191 9.2% Mark Brown 643 5.0% Alex Deucher 530 4.1% Martin K. Petersen 318 2.5% Andrew Morton 304 2.4% Mauro Carvalho Chehab 222 1.7% Ingo Molnar 209 1.6% Michael Ellerman 208 1.6% Jason Gunthorpe 194 1.5% Jens Axboe 187 1.5% Jonathan Cameron 177 1.4% Jonathan Corbet 173 1.3% Herbert Xu 165 1.3% Alexei Starovoitov 149 1.2% Jeff Kirsher 146 1.1% David Sterba 143 1.1% Hans Verkuil 140 1.1% Shawn Guo 138 1.1% Daniel Borkmann 126 1.0%

Employers Red Hat 2256 17.5% Linux Foundation 1255 9.7% Linaro 1231 9.6% Intel 1045 8.1% Google 704 5.5% AMD 556 4.3% (None) 417 3.2% Mellanox 397 3.1% IBM 394 3.1% Facebook 394 3.1% SUSE 382 3.0% Oracle 357 2.8% ARM 333 2.6% Huawei Technologies 330 2.6% Samsung 322 2.5% (Unknown) 246 1.9% Bootlin 198 1.5% LWN.net 173 1.3% Code Aurora Forum 146 1.1% (Consultant) 141 1.1%

The concentration of subsystem maintainers into a small number of companies has spread out over time, but it is still true that (just) over 50% of the non-author signoffs are made by developers working in five companies.

Code longevity

Finally, it has been a while since we have looked at how much code from each development cycle remains in the 5.2 kernel. This determination is made through the application of a fair amount of brute force: for each file in the kernel tree, git blame is run and the commit that added each line is noted. After associating each commit with the development cycle that brought it into the mainline, it is possible to see how many lines of code were introduced by each cycle. The results look like this:

As can be seen here, newer releases are more heavily represented than older ones, which is not surprising. There has been more time for changes to be made to code from older releases, and more recent cycles tend to add more lines in general. Still, it seems clear that a lot of the code we add stays in the kernel for a long time.

The most graphic illustration of that, actually, does not appear in the graph because it would squeeze the rest into insignificance: over 2.5 million lines of code in the kernel — nearly 10% of the total — date back to the initial Git commit in 2005. Much of that code was old even then, and certainly hasn't gotten any younger.

Stepping back one release, there are 215 files in 5.1 that have not seen a single change since the initial commit. This number can only undercount the number of dormant files by a significant factor: any file that has seen even a single whitespace fix, coding-style change, or typo fix will not appear in this list. Indeed, the list was generated from the 5.1 kernel because the SPDX work in 5.2 is obscuring things further. These files may get shiny new license tags, but that won't make them any more alive.

Code that is this old perhaps just reached perfection years ago and needs no further changes. In general, though, static code is often unmaintained, unused, and possibly insecure. For anybody looking to do a little cleanup work, this list might not be a bad place to start.

Index entries for this article
Kernel	Releases/5.2