Statistics for the 2.6.36 development cycle

As this is being written, the last 2.6.36 prepatch has (with luck) been released and the final release can be expected within a few days. So it is time to have a look at how this development cycle has gone. There are a couple of things which distinguish 2.6.36 from its predecessors in interesting ways.

The 2.6.36 kernel will incorporate about 9400 changesets contributed by 1159 developers. It thus continues a recent trend toward less active development cycles; here is what we have seen over the course of the last year or so:

Release	Changes
2.6.31	10,883
2.6.32	10,998
2.6.33	10,871
2.6.34	9,443
2.6.35	9,801
2.6.36	~9,400

The work which pushed up the changeset numbers in previous development cycles (shoveling out-of-tree code into the staging directory being at the top of the list) continues to wind down, as does work in other areas (like new filesystems). As a result, the kernel is going through a period of relatively low flux - but only relative to the last couple of years - and stabilization. That said, it's worth noting that, unless something unexpected happens, the 2.6.36 development cycle will be one of the shortest in recent memory; as a result, the number of changesets merged per day is the highest since 2.6.30.

Perhaps more interesting is this set of numbers: in 2.6.36, the development community added 604,000 lines of code and deleted 651,000 - for a total loss of almost 47,000 lines of code. This is the first time since the beginning of the git era that the size of the kernel source has gone down. Given that, perhaps it is appropriate to start with a look at who has been so busily removing code from the kernel:

Most lines removed - 2.6.36
Sam Ravnborg	205813	31.6%
Benjamin Herrenschmidt	133666	20.5%
Amerigo Wang	19145	2.9%
Tony Luck	8418	1.3%
Greg Kroah-Hartman	7094	1.1%
Kiran Divekar	4487	0.7%
Palash Bandyopadhyay	4457	0.7%
Vincent Sanders	3467	0.5%
Dave Jones	2600	0.4%
Christoph Hellwig	2163	0.3%

Sam Ravnborg and Ben Herrenschmidt both got to the top of the list through the removal of a bunch of defconfig files, part of a general cleanup inspired by some grumpiness from Linus back in June; Sam also finished up some SPARC unification work. Amerigo Wang removed a number of old and unused drivers. Between the three of them, they got rid of almost 360,000 lines of code - a laudable bit of work.

Looking at code changes in general for the 2.6.36 development cycle yields this picture:

Most active 2.6.36 developers

By changesets Vasiliy Kulikov 160 1.7% Eric Paris 124 1.3% Dan Carpenter 122 1.3% Chris Wilson 117 1.3% Eric Dumazet 108 1.2% Uwe Kleine-König 103 1.1% Axel Lin 98 1.0% Johannes Berg 97 1.0% Al Viro 96 1.0% Julia Lawall 89 1.0% Tejun Heo 88 0.9% Joe Perches 83 0.9% Christoph Hellwig 73 0.8% Alex Deucher 71 0.8% Ben Skeggs 69 0.7% John W. Linville 68 0.7% Stefan Richter 64 0.7% Stephen M. Cameron 62 0.7% Felix Fietkau 60 0.6% Randy Dunlap 59 0.6%

By changed lines Sam Ravnborg 208270 19.4% Benjamin Herrenschmidt 134811 12.5% Chris Metcalf 53204 4.9% Omar Ramirez Luna 51087 4.8% Amerigo Wang 19191 1.8% Jarod Wilson 16020 1.5% Felix Fietkau 11898 1.1% Alan Olsen 11650 1.1% Mike Thomas 11087 1.0% Lars-Peter Clausen 10795 1.0% Tony Luck 9351 0.9% Tetsuo Handa 7955 0.7% Casey Leedom 7888 0.7% John Johansen 7591 0.7% Greg Kroah-Hartman 7195 0.7% Charles Clément 6864 0.6% Dmitry Kravkov 6754 0.6% Kiran Divekar 6753 0.6% Ben Collins 6540 0.6% Christoph Hellwig 6045 0.6%

On the changesets side, Vasiliy Kulikov leads with a long list of mostly small fixes, mostly in device driver code. The bulk of Eric Paris's work is the addition of the fanotify subsystem - work which, as of this writing, will not be enabled for the 2.6.36 release due to user-space ABI concerns. Dan Carpenter is another master of small fixes, usually for problems identified by static analysis tools. Chris Wilson had a large number of changes to the Intel i915 driver - and seemingly an even larger number fixing the resulting problems. Eric Dumazet's changes were a large number of fixes and improvements to the networking subsystem.

Three of the top five in the "lines changed" column have already been mentioned above. The other two are Chris Metcalf, who added the new "Tile" architecture, and Omar Ramirez Luna, who added the TI dspbridge driver to the staging tree.

Only one top-five developer (Dan Carpenter) was also in the top five for 2.6.35; there are a lot of new faces on the list this time around.

There were 184 employers (that we could identify) who contributed code to the 2.6.36 kernel. The top corporate supporters were:

Most active 2.6.36 employers

By changesets (None) 1524 16.3% Red Hat 1129 12.1% (Unknown) 865 9.2% Intel 691 7.4% Novell 404 4.3% IBM 374 4.0% Nokia 212 2.3% Texas Instruments 189 2.0% (Academia) 178 1.9% Samsung 178 1.9% Fujitsu 160 1.7% NTT 151 1.6% Pengutronix 145 1.6% AMD 131 1.4% Google 125 1.3% (Consultant) 109 1.2% Societe Francaise de Radiotelephone 108 1.2% QLogic 107 1.1% Atheros Communications 99 1.1% MiTAC 98 1.0%

By lines changed (None) 299115 27.8% IBM 151386 14.1% Red Hat 76455 7.1% (Unknown) 71662 6.7% Tilera 64825 6.0% Texas Instruments 63521 5.9% Intel 55167 5.1% Novell 25798 2.4% Samsung 14619 1.4% NTT 12187 1.1% Marvell 10769 1.0% Chelsio 10560 1.0% (Academia) 10345 1.0% QLogic 9873 0.9% Google 9503 0.9% Broadcom 8391 0.8% ST Ericsson 8390 0.8% Canonical 8354 0.8% Nokia 8060 0.7% Atheros Communications 7762 0.7%

For the most part, this list looks the way it has for most development cycles, but there are a couple of new names here. One is Tilera, the company behind the Tile architecture, which got its support merged for 2.6.36. The other name appearing here for the first time is Canonical, which got the AppArmor security module code merged at last. Meanwhile, one should not forget the other 164 companies which do not appear on the above list; the commercial ecosystem around the Linux kernel remains strong and diverse.

Finally, your editor decided to rerun an old experiment to look at the longevity of code in the kernel. Every line in the kernel source was mapped back to the kernel release where it was last changed, then the totals for each release were plotted. The resulting picture looks like this:

At 1.6% of the total, 2.6.36 represents a relatively small piece of the total code base - the smallest for a long time. Almost 29% of the kernel code still dates back to the beginning of the git era, down from 31% last February. While much of our kernel code is quite new - 31% of the code comes from 2.6.30 or newer - much of it has also hung around for a long time.

All told, 2.6.36 was a relaxed development cycle with relatively few big new features and a fair amount of cleanup. That is certainly part of how it was able to be stabilized in a shorter-than-usual period, and with fewer than the usual number of regressions (56 reported as of October 10, as opposed to 100 for 2.6.35-rc6). Whether 2.6.36 represents a new norm for a slightly slower kernel development process remains to be seen. As of this writing, the linux-next tree contains 5850 changesets, most of which are presumably intended for 2.6.37. Quite a few changes still typically do not appear in linux-next prior to the opening of the merge window, so we should see more changes than that merged for 2.6.37. Still, current linux-next does not look like a huge wave of pent-up changes waiting to fly into the mainline; 2.6.37 may or may not exceed 2.6.36 in the number of changes, but it does not look like it will be breaking any records.

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