The 6.13 development cycle ended on January 19 with the release of the 6.13 kernel. This cycle was, on its surface, one of the slowest we have seen in some time; the LWN merge-window summaries (part 1, part 2) and the KernelNewbies 6.13 page can be consulted for a refresher on all it contains. Here, instead, we will take our usual look at where all of those changes came from.

The 6.13 kernel cycle brought in 12,928 non-merge changesets from 2,001 developers. The changeset count is noteworthy for being the lowest since 5.15 (12,377 changesets) in 2021. If one looks at a plot of changeset traffic for each kernel release (taken from the LWN Kernel Source Database), one sees:

The immediate impression is that kernel development activity has gone into a decline since the 6.7 release (January 2024) hit a record with 17,284 changesets. Interestingly, though, a plot of the number of developers participating in each release tells a slightly different story:

The 2,001 developers who contributed to 6.13 are somewhat short of the record (2,090) set with 6.2 in 2023, but the previous release (6.12, at 2,074 developers) came close. Kernel developers may be merging fewer changesets at the moment, but that does not necessarily mean that less work is being done and, in any case, there are as many people working on the kernel as there has ever been.

The most active developers this time around were:

Most active 6.13 developers

By changesets Thomas Zimmermann 185 1.4% Andy Shevchenko 158 1.2% Sean Christopherson 147 1.1% Jani Nikula 142 1.1% Darrick J. Wong 113 0.9% Christoph Hellwig 112 0.9% Dmitry Baryshkov 111 0.9% Javier Carrasco 111 0.9% Thomas Weißschuh 102 0.8% Ian Rogers 99 0.8% Dr. David Alan Gilbert 91 0.7% Thomas Gleixner 90 0.7% Philipp Hortmann 84 0.6% Ville Syrjälä 82 0.6% Masahiro Yamada 81 0.6% Uwe Kleine-König 80 0.6% Dmitry Torokhov 80 0.6% Bartosz Golaszewski 79 0.6% Mark Brown 79 0.6% Kuniyuki Iwashima 78 0.6%

By changed lines Philipp Hortmann 76407 10.0% Jan Kara 32830 4.3% Dave Penkler 29327 3.8% Johannes Berg 26104 3.4% Dmitry Baryshkov 11847 1.6% Bitterblue Smith 10591 1.4% Daniel Machon 9878 1.3% Hans Verkuil 9490 1.2% Marek Vasut 8282 1.1% Detlev Casanova 8121 1.1% Andy Shevchenko 7755 1.0% Darrick J. Wong 7566 1.0% Konrad Dybcio 6661 0.9% Taniya Das 5891 0.8% Ian Rogers 5831 0.8% Dr. David Alan Gilbert 5570 0.7% Ivaylo Ivanov 5469 0.7% Tomi Valkeinen 5278 0.7% Jani Nikula 5038 0.7% Zong-Zhe Yang 4832 0.6%

Thomas Zimmermann topped the by-changesets column with a long list of improvements throughout the graphics subsystem. Andy Shevchenko contributed refactoring and cleanups over much of the driver subsystem. Sean Christopherson continued the ongoing refactoring of the KVM subsystem. Jani Nikula contributed many changes to the Intel i915 graphics driver, and Darrick Wong worked extensively in the XFS filesystem, with much of that work going toward online filesystem-checking functionality.

In the lines-changed column, Philipp Hortmann removed a number of old wireless-network drivers. Jan Kara removed the ReiserFS filesystem. Dave Penkler added the GPIB driver subsystem to the staging tree. Johannes Berg also joined the wireless-driver-removal party, and Dmitry Baryshkov added support for a number of Qualcomm clocks.

If the 6.13 development was a bit quieter than usual, some of the reasons why can be seen in the above list. The extensive refactoring work that has created large changeset counts in previous kernels is mostly absent this time around. The massive amdgpu header-file contributions that have bloated past kernels are also not present in 6.13. Instead, we are seeing the steady pace of development that is always happening, but which can be obscured in the statistics by those larger changes.

Just over half (51.3%) of the commits merged for 6.13 included at least one Reviewed-by tag, but only 8% had Tested-by tags. The top testers and reviewers in 6.13 were:

Test and review credits in 6.13

Tested-by Daniel Wheeler 148 11.9% Dmitry Osipenko 85 6.8% Alex Bennée 55 4.4% Neil Armstrong 47 3.8% Pucha Himasekhar Reddy 30 2.4% Gary Guo 19 1.5% Nathan Chancellor 15 1.2% Randy Dunlap 15 1.2% Nicolin Chen 14 1.1% Serge Semin 13 1.0% Steev Klimaszewski 13 1.0% Philipp Zabel 12 1.0% Chris Healy 12 1.0% Leo Yan 11 0.9% Geert Uytterhoeven 10 0.8% Rob Clark 10 0.8% Rajneesh Bhardwaj 10 0.8% Arnaldo Carvalho de Melo 10 0.8%

Reviewed-by Christoph Hellwig 216 2.5% Simon Horman 211 2.4% Krzysztof Kozlowski 197 2.3% Dmitry Baryshkov 119 1.4% Ilpo Järvinen 112 1.3% Eric Dumazet 111 1.3% Rodrigo Vivi 95 1.1% Rob Herring 94 1.1% Darrick J. Wong 91 1.1% Andy Shevchenko 91 1.1% AngeloGioacchino Del Regno 86 1.0% Geert Uytterhoeven 84 1.0% Neil Armstrong 81 0.9% Ville Syrjälä 81 0.9% David Sterba 78 0.9% Jason Gunthorpe 78 0.9% Christian König 76 0.9% Laurent Pinchart 75 0.9%

These results do not change much from one release to the next; the people who do this work are in it for the long haul. LWN subscribers may see this KSDB page for more information on the testers, reviewers, and bug reporters for 6.13.

Work on 6.13 was supported by 212 employers (that we know of), a typical number. The top employers were:

Most active 6.13 employers

By changesets Intel 1482 11.4% (Unknown) 1143 8.8% Google 977 7.5% Red Hat 698 5.4% AMD 644 5.0% Linaro 626 4.8% (None) 586 4.5% SUSE 422 3.3% Huawei Technologies 382 2.9% Meta 344 2.6% Oracle 340 2.6% IBM 316 2.4% Qualcomm 271 2.1% Renesas Electronics 257 2.0% NVIDIA 231 1.8% NXP Semiconductors 225 1.7% Linutronix 212 1.6% Arm 210 1.6% BayLibre 206 1.6% (Consultant) 199 1.5%

By lines changed (Unknown) 91599 12.0% Intel 82247 10.8% Emerson 76407 10.0% SUSE 42347 5.5% Qualcomm 39053 5.1% Linaro 31638 4.1% Google 30487 4.0% AMD 28441 3.7% Red Hat 26727 3.5% (None) 24370 3.2% Oracle 15285 2.0% Meta 15114 2.0% Collabora 14973 2.0% IBM 13880 1.8% Microchip Technology Inc. 13658 1.8% Realtek 12685 1.7% NVIDIA 11718 1.5% BayLibre 10654 1.4% Cisco 9864 1.3% NXP Semiconductors 9185 1.2%

Here, too, there are not many surprises to be found.

There were a number of significant changes in 6.13; the addition of lazy preemption and a lot of important Rust infrastructure may, over time, come to be seen as some of the most important. But the removals this time around are also significant. ReiserFS was once the brightest light among Linux filesystems; it was the first to bring journaling, among other things. It has long since been surpassed and gone out of use, but its role should not be forgotten.

The removal of the old wireless drivers also marks the end of an era of sorts. When Linux first started supporting wireless network interfaces, they were treated much like Ethernet interfaces with a few extra parameters to tweak. The "wireless extensions" interface was added to enable that tweaking. It did not take long to realize that wireless interfaces needed to be treated as a different class of device, and the networking subsystem moved in that direction. But the wireless extensions, as a user-facing interface, had to be supported for many years despite its inability to perform all of the necessary management functions for modern network adapters. Only with 6.13 has it been possible, finally, to remove that support.

ReiserFS was introduced in 2.4.0.4 in 2001, and the wireless extensions came with 2.1.15 in 1996. This kernel release, too, surely includes code that will come to be seen, decades from now, as outmoded and ready for removal. But there will be code to replace it; as of this writing, there are just short of 9,000 changesets in linux-next waiting to be merged for 6.14. That release, too, seems unlikely to set any records for change volume. Even below its peak rate, though, the kernel community is a busy place.

Index entries for this article
Kernel	Releases/6.13

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git log -M -C -D --author="Andy Shevchenko" --ignore-all-space --pretty="" --numstat v6.12..v6.13
awk RS="\n" {
	 	 for (i=0; i < int(NF / 3); i++) {
	 	 	 sum += $(3*i+1) + $(3*i+2)
	 	 }
	 } END { print sum }