Some numbers from the 4.6 development cycle

With the 4.6-rc7 release on May 8, the 4.6 kernel is nearly ready for release. It wouldn't be a proper development cycle without a set of statistics showing where the code came from this time around. With the 4.6 kernel we have seen some old names return to the lists of the top contributors, but, for the most part, it looks like a typical — if busy — cycle.

The 4.6 merge window, with 12,172 non-merge commits, was the busiest in the history of the kernel project. By current appearances, though, 4.6 will not be setting the record for the busiest development cycle overall. The 13,354 commits merged up to 4.6-rc7 are a lot, but it seems unlikely that the total when 4.6-final comes out will exceed the 13,694 merged for 4.2, much less the 13,722 merged for 3.15. So the record set for 3.15 will, at the beginning of June, have held for a full two years.

Those commits were contributed by 1,661 developers, which is a new record, beating the 1,625 seen contributing to 4.3. 283 of those developers made their first commit to the kernel during this development cycle. The most active 4.6 developers were:

Most active 4.6 developers

By changesets Arnd Bergmann 204 1.5% Chaehyun Lim 197 1.5% Oleg Drokin 165 1.2% Jes Sorensen 131 1.0% Amitoj Kaur Chawla 117 0.9% Christian König 107 0.8% Dennis Dalessandro 100 0.7% Mauro Carvalho Chehab 97 0.7% Al Viro 93 0.7% Peter Hurley 91 0.7% Linus Walleij 86 0.6% Geert Uytterhoeven 86 0.6% Laxman Dewangan 85 0.6% Andy Lutomirski 84 0.6% Marc Zyngier 84 0.6% Laurent Pinchart 84 0.6% Namhyung Kim 81 0.6% Mike Rapoport 81 0.6% Bhaktipriya Shridhar 80 0.6% Tomi Valkeinen 78 0.6%

By changed lines Faisal Latif 28327 4.3% Dennis Dalessandro 16034 2.4% Mike Marshall 15434 2.3% Shraddha Barke 14126 2.1% Oleg Drokin 7935 1.2% Josh Poimboeuf 7917 1.2% Andrew Duggan 6640 1.0% John Crispin 5914 0.9% Tomi Valkeinen 5893 0.9% Archit Taneja 5704 0.9% Andrew F. Davis 5513 0.8% Jiri Pirko 5410 0.8% Santosh Shilimkar 5338 0.8% Alexandre Bounine 5191 0.8% Yuval Mintz 5054 0.8% James Simmons 4619 0.7% Laurent Pinchart 4534 0.7% Mauro Carvalho Chehab 4533 0.7% Sudeep Dutt 4387 0.7% Marc Zyngier 4230 0.6%

Longtime kernel developer Arnd Bergmann found his way to the top of the "by changesets" column mainly through his ongoing work to eliminate warnings from the ARM kernel builds. Chaehyun Lim continues to work on the wilc1000 staging driver, Oleg Drokin did a lot of cleanups in the Lustre filesystem, Jes Sorensen continues to clean up the rtl8xxxu staging driver, and Amitoj Kaur Chawla made cleanups throughout the driver subsystem.

On the "lines changed" side, Faisal Latif got to the top of the list with the addition of the i40iw InfiniBand driver. Dennis Dalessandro worked on various RDMA drivers, Mike Marshall added the OrangeFS filesystem, and Shraddha Barke removed some unloved drivers from the staging tree.

The number of employers seen supporting kernel work remains steady at just over 200; this count has not changed significantly since the early 3.x days. The most active employers in this cycle were:

Most active 4.6 employers

By changesets Intel 2009 15.0% (Unknown) 1358 10.2% Red Hat 1043 7.8% (None) 647 4.8% Linaro 588 4.4% Outreachy 413 3.1% Samsung 390 2.9% SUSE 364 2.7% Renesas Electronics 336 2.5% IBM 312 2.3% AMD 307 2.3% ARM 253 1.9% Google 247 1.8% (Consultant) 238 1.8% Texas Instruments 230 1.7% Oracle 191 1.4% Code Aurora Forum 175 1.3% Atmel 166 1.2% NVidia 159 1.2% Huawei Technologies 147 1.1%

By lines changed Intel 131992 20.0% (Unknown) 43271 6.5% Red Hat 40589 6.1% (None) 29098 4.4% Linaro 19259 2.9% IBM 17455 2.6% Outreachy 17445 2.6% Omnibond Systems 17122 2.6% Texas Instruments 16779 2.5% Code Aurora Forum 14484 2.2% Renesas Electronics 14222 2.2% Google 14183 2.1% AMD 13581 2.1% SUSE 12304 1.9% Samsung 12107 1.8% Oracle 11441 1.7% Mellanox 10971 1.7% ARM 10811 1.6% Facebook 9642 1.5% (Consultant) 8086 1.2%

As usual, little has changed in this table. Lots of cleanup patches made their way into the staging tree as part of the application process for Outreachy internships; this time around, some of the Outreachy interns are employing Coccinelle scripts and increasing their productivity accordingly. One name that might be unfamiliar is Omnibond Systems — the company behind OrangeFS. Otherwise, it's mostly the names one usually sees in this place.

Reviewing Reviewed-by

Finally, let's take a quick look at Reviewed-by counts. A developer can offer a Reviewed-by tag after having reviewed a patch in depth; these tags are considered a sign that the patches in question have been closely examined and are of high quality. They are also there to credit the developers who spend time reviewing code — an important objective, since review bandwidth is one of the community's most limited resources. In the 4.6 development kernel, a total of 3,645 Reviewed-by tags were applied to patches; the most prolific sources of them were:

Most active 4.6 reviewers
Alex Deucher	155	4.3%
Mike Marciniszyn	141	3.9%
Ira Weiny	133	3.6%
Dennis Dalessandro	130	3.6%
Christoph Hellwig	98	2.7%
Hannes Reinecke	91	2.5%
Johannes Thumshirn	82	2.2%
Oleg Drokin	77	2.1%
Daniel Vetter	72	2.0%
Ville Syrjälä	68	1.9%
Krzysztof Kozlowski	64	1.8%
Christoffer Dall	54	1.5%
Christian König	53	1.5%
Thomas Gleixner	49	1.3%
Chris Wilson	47	1.3%
Dean Luick	44	1.2%
Maarten Lankhorst	41	1.1%
James Simmons	40	1.1%
Chunming Zhou	37	1.0%
Laurent Pinchart	36	1.0%

This table makes it clear that different developers have different views of how Reviewed-by should be used. The top reviewer is Alex Deucher, the maintainer for the AMD graphics drivers. Alex certainly reviews a lot of patches; in this case, though, most of the patches with his Reviewed-by tags also carried his Signed-off-by tags — applied when he accepted the patches for merging. It is normally understood that maintainers should review patches before applying them; most maintainers do not add a Reviewed-by tag for that work, but Alex does.

Out of the next three reviewers on the list, Mike Marciniszyn, Ira Weiny, and Dennis Dalessandro, only Mike appears in the MAINTAINERS file. They do have something in common, though, in that they all work for Intel. Patches generally come out of Intel with Reviewed-by tags from these developers (among others), often all three together, applied before the code has been seen by the rest of the world. We are clearly seeing the results of some sort of internal Intel review policy at work. There is no real way to know how thorough this review process is, other than to observe that Intel contributes a lot of patches and problems are rare.

The fifth entry in the list, Christoph Hellwig, typifies the sort of review that was envisioned when this tag was created. Nobody who has had Christoph's attention applied to a patch of theirs will have missed the fact that a serious review has taken place. The work of the other four reviewers named above may well be just as thorough and just as valuable, but, since it's not public review, there is no way to know for sure.

Of course, almost all of the review work that does take place in public still does not result in a Reviewed-by tag being applied to the patches involved. So it could be argued that this tag has never really achieved its purpose of documenting and crediting the review work that is being done.

The overall picture created by these numbers, though, is one of a development process that continues to function like a relatively well-tuned machine. The number of contributors continues to increase, the patch flow is steady, and there do not appear to be many process-scalability issues in sight.

Index entries for this article
Kernel	Releases/4.6

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