Some numbers from the 3.11 development cycle

As of this writing, the 3.11-rc6 prepatch is out and the 3.11 development cycle appears to be slowly drawing toward a close. That can only mean one thing: it must be about time to look at some statistics from this cycle and see where the contributions came from. 3.11 looks like a fairly typical 3.x cycle, but, as always, there's a small surprise or two for those who look.

Developers and companies

Just over 10,700 non-merge changesets have been pulled into the repository (so far) for 3.11; they added over 775,000 lines of code and removed over 328,000 lines for a net growth of 447,000 lines. So this remains a rather slower cycle than 3.10, which was well past 13,000 changesets by the -rc6 release. As might be expected, the number of developers contributing to this release has dropped along with the changeset count, but this kernel still reflects contributions from 1,239 developers. The most active of those developers were:

Most active 3.11 developers

By changesets H Hartley Sweeten 333 3.1% Sachin Kamat 302 2.8% Alex Deucher 254 2.4% Jingoo Han 190 1.8% Laurent Pinchart 147 1.4% Daniel Vetter 137 1.3% Al Viro 131 1.2% Hans Verkuil 123 1.1% Lee Jones 112 1.0% Xenia Ragiadakou 100 0.9% Wei Yongjun 99 0.9% Jiang Liu 98 0.9% Lars-Peter Clausen 91 0.8% Linus Walleij 90 0.8% Johannes Berg 86 0.8% Tejun Heo 85 0.8% Oleg Nesterov 71 0.7% Fabio Estevam 70 0.7% Tomi Valkeinen 69 0.6% Dan Carpenter 66 0.6%

By changed lines Peng Tao 260439 26.9% Greg Kroah-Hartman 91973 9.5% Alex Deucher 55904 5.8% Kalle Valo 22103 2.3% Ben Skeggs 20282 2.1% Eli Cohen 15886 1.6% Solomon Peachy 15510 1.6% Aaro Koskinen 13443 1.4% H Hartley Sweeten 11043 1.1% Laurent Pinchart 8923 0.9% Benoit Cousson 8734 0.9% Tomi Valkeinen 8246 0.9% Yuan-Hsin Chen 8222 0.9% Tomasz Figa 7668 0.8% Xenia Ragiadakou 5136 0.5% Johannes Berg 5029 0.5% Maarten Lankhorst 4924 0.5% Marc Zyngier 4817 0.5% Hans Verkuil 4707 0.5% Linus Walleij 4379 0.5%

Someday, somehow, somebody will manage to displace H. Hartley Sweeten from the top of the by-changesets list, but that was not fated to be in the 3.11 cycle. As always, he is working on cleaning up the Comedi drivers in the staging tree — a task that has led to the merging of almost 4,000 changesets into the kernel so far. Sachin Kamat contributed a large set of cleanups throughout the driver tree, Alex Deucher is the primary developer for the Radeon graphics driver, Jingoo Han, like Sachin, did a bunch of driver cleanup work, and Laurent Pinchart did a lot of Video4Linux and ARM architecture work.

On the "lines changed" side, Peng Tao added the Lustre filesystem to the staging tree, while Greg Kroah-Hartman removed the unloved csr driver from that tree. Alex's Radeon work has already been mentioned; Kalle Valo added the ath10k wireless network driver, while Ben Skeggs continued to improve the Nouveau graphics driver.

Almost exactly 200 employers supported work on the 3.11 kernel; the most active of those were:

Most active 3.11 employers

By changesets (None) 976 9.1% Intel 970 9.1% Red Hat 911 8.5% Linaro 890 8.3% Samsung 485 4.5% (Unknown) 483 4.5% IBM 418 3.9% Vision Engraving Systems 333 3.1% Texas Instruments 319 3.0% SUSE 310 2.9% AMD 281 2.6% Renesas Electronics 265 2.5% Outreach Program for Women 230 2.1% Google 224 2.1% Freescale 151 1.4% Oracle 137 1.3% ARM 135 1.3% Cisco 132 1.2%

By lines changed (None) 307996 31.9% Linux Foundation 93929 9.7% AMD 57745 6.0% Red Hat 52679 5.5% Intel 40868 4.2% Texas Instruments 28819 3.0% Qualcomm 26215 2.7% Renesas Electronics 24084 2.5% Samsung 23413 2.4% Linaro 20649 2.1% (Unknown) 17362 1.8% IBM 17337 1.8% AbsoluteValue Systems 16872 1.7% Nokia 16847 1.7% Mellanox 16841 1.7% Vision Engraving Systems 12268 1.3% Outreach Program for Women 11499 1.2% SUSE 10279 1.1%

Once again, the percentage of changes coming from volunteers (listed as "(None)" above) appears to be slowly falling; it is down from over 11% in 3.10. Red Hat has, for the second time, ceded the top non-volunteer position to Intel, but the fact that Linaro is closing on Red Hat from below is arguably far more interesting. The numbers also reflect the large set of contributions that came in from applicants to the Outreach Program for Women, which has clearly succeeded in motivating contributions to the kernel.

Signoffs

Occasionally it is interesting to look at the Signed-off-by tags in patches in the kernel repository. In particular, if one looks at signoffs by developers other than the author of the patch, one gets a sense for who the subsystem maintainers responsible for getting patches into the mainline are. In the 3.11 cycle, the top gatekeepers were:

Most non-author signoffs in 3.11

By developer Greg Kroah-Hartman 1212 12.3% David S. Miller 801 8.1% Andrew Morton 611 6.2% Mauro Carvalho Chehab 371 3.8% John W. Linville 285 2.9% Mark Brown 276 2.8% Daniel Vetter 264 2.7% Simon Horman 252 2.6% Linus Walleij 236 2.4% Benjamin Herrenschmidt 172 1.7% Kyungmin Park 157 1.6% James Bottomley 143 1.4% Ingo Molnar 132 1.3% Rafael J. Wysocki 131 1.3% Kukjin Kim 121 1.2% Dave Airlie 121 1.2% Shawn Guo 121 1.2% Felipe Balbi 119 1.2% Johannes Berg 117 1.2% Ralf Baechle 110 1.1%

By employer Red Hat 2156 21.9% Linux Foundation 1249 12.7% Intel 904 9.2% Google 788 8.0% Linaro 759 7.7% Samsung 429 4.4% (None) 408 4.1% IBM 332 3.4% Renesas Electronics 259 2.6% SUSE 249 2.5% Texas Instruments 237 2.4% Parallels 143 1.5% Wind River 126 1.3% (Unknown) 124 1.3% Wolfson Microelectronics 114 1.2% Broadcom 97 1.0% Fusion-IO 89 0.9% OLPC 87 0.9% (Consultant) 86 0.9% Cisco 80 0.8%

We first looked at signoffs for 2.6.22 in 2007. Looking now, there are many of the same names on the list — but also quite a few changes. As is the case with other aspects of kernel development, the changes in signoffs reflect the growing importance of the mobile and embedded sector. The good news, as reflected in these numbers, is that mobile and embedded developers are finding roles as subsystem maintainers, giving them a stronger say in the direction of kernel development going forward.

Persistence of code

Finally, it has been some time since we looked at persistence of code over time; in particular, we examined how much code from each development cycle remained in the 2.6.33 kernel. This information is obtained through the laborious process of running "git blame" on each file, looking at the commit associated with each line, and mapping that to the release in which that commit was merged. Doing the same thing now yields a plot that looks like this:

From this we see that the code added for 3.11 makes up a little over 4% of the kernel as a whole; as might be expected, the percentage drops as one looks at older releases. Still, quite a bit of code from the early 2.6.30's remains untouched to this day. Incidentally, about 19% of the code in the kernel has not been changed since the beginning of the git era; there are still 545 files that have not been changed at all since the 2.6.12 development cycle.

Another way to look at things would be to see how many lines from each cycle were in the kernel in 2.6.33 (the last time this exercise was done) compared to what's there now. That yields:

Thus, for example, the 2.6.33 kernel had about 400,000 lines from 2.6.26; of those, about 290,000 remain in 3.11. One other thing that stands out is that the early 2.6.30 development cycles saw fewer changesets merged into the mainline than, say, 3.10 did, but they added more code. Much of that code has since been changed or removed, though. Given that much of that code went into the staging tree, this result is not entirely surprising; the whole point of putting code into staging is to set it up for rapid change.

Actually, "rapid change" describes just about all of the data presented here. The kernel process continues to absorb changes at a surprising and, seemingly, increasing rate without showing any serious signs of strain. There is almost certainly a limit to the scalability of the current process, but we do not appear to have found it yet.

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