Session:The Kernel Report ELC 2012

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Session Details

ELC 2012
February 15, 2012
Jonathan Corbet
The Kernel Report ELC 2012
here (linux foundation) and here (free-electrons)
58 minutes


The Linux kernel is at the core of any Linux system; the performance and capabilities of the kernel will, in the end, place an upper bound on what the system as a whole can do. This talk will review recent events in the kernel development community, discuss the current state of the kernel and the challenges it faces, and look forward to how the kernel may address those challenges. Attendees of any technical ability should gain a better understanding of how the kernel got to its current state and what can be expected in the near future.


Jonathan Corbet got his first look at the BSD Unix source back in 1981, when an instructor at the University of Colorado let him "fix" the paging algorithm. He has been digging around inside every system he could get his hands on ever since, working on drivers for VAX, Sun, Ardent, and x86 systems on the way. He got his first Linux system in 1993, and has never looked back. Mr. Corbet is currently the co-founder and executive editor of Linux Weekly News; he lives in Boulder, Colorado with his wife and two children.



Transcribed by
Chris Dudding

0:00 - 1:00:

[ELC Slide - Thank you to our sponsors]

>> INTRODUCER: So, I'd like to welcome you all out to this year's Embedded Linux conference. Very happy to see you all here and I hope you're as anxious as I am.

We're.. well erm. anxious is not the right word but excited as I am about the great sessions we've got planned for this week. Um..

This is always erm.. the best part of getting ready for a conference is when you actually get the thing under way and there's been a lot of prep work behind the scenes and we're very excited to have you here and excited about the programme we've got.

[ELC Slide - Mobile App]

I've got just a couple of quick announcements I'd like to make:

First, about the mobile application so in the guide it talks about a mobile app um.. the actual name you look for in the marketplace is wrong in the guide

1:00 - 2:00:

You need to look under Linux Foundation conference. And that's available on the Android Market. There's actually a kind of a funny story why its not available for iPhone and that was because when it was first submitted to the iPhone erm. I don't know what they call their..

>> AUDIENCE: App Store

[Laughter] Well, so. Yes, thank you. It actually it was for.. It had Android listed in the description because it covers both conferences: Android Developers.. [rephrases] Android Builders Submit and ELC and they rejected it because of the word Android. So, go figure!

So, not for lack of trying. I'm sorry we don't have an iPhone app for you. Get yourself a more open phone! [Laughter]

[ELC Slide - Intel Atom Processor Giveaway]

Anyway, also I'd like to talk about this. So this um.. [holds Intel Atom development board] Ignore the antennas. Inside is a little development board

2:00 - 3:00:

that is being manufactured by Intel and it contains an Atom processor. Its actually called the.. I love Intel code names.. the board is called a Fish River Island 2 and its erm. E6XX Tunnel Creek Processor and they will be manufacturing these.. these are not available yet. They will be manufacturing 'em and sending them out to attendees. If you are interested in getting one.. we have.. unfortunately we don't have enough for everyone but what they are doing is they are taking proposals you can register at the Intel desk just outside in the lobby. And kind of just give an idea what you would plan to do with the board and the first 120 good ideas will get one shipped to you sometime in April or May. So, that's pretty nice. Let's thank Intel for that. [Claps] So that's pretty nice. Um.. So that's pretty cool

3:00 - 4:00:

Nice little development board for you [inaudible comment from audience] [laughs] No, too low.

and let's see I want to mention the YOCTO reception, hosted by YOCTO and Intel is reception tonight. Should be a lot of fun. Its over at the hiller aviation museum and there's a little.. cute little boarding pass thing you got talking about that also we've got little stickers done by jambe that you can get if you want to proudly proclaim that you came to ELC

and the last thing to do is to introduce our keynote speaker for this morning. So, I've known Jon Corbet for a number of years. He's kind of.. I don't know if this is the right term because he has no beard.. he's one of the grey beards in the Linux industry and an incredible incredible asset

4:00 - 5:00:

At these events it is very customary for us to put in a plug for and this event is no exception. In my opinion one of the premier sources for information about Linux, the Linux kernel and the industry and open source.

If you are not a subscribing member of, you should be one.. shame on you.. because this is an asset. Really a community asset that we should support and Jon very graciously accepted to give our kernel report and he'll tell us all about what's going on with the kernel in the last little bit and maybe a little bit about what's coming up in the future

So without further ado, let me introduce Jon Corbet.

5:00 - 6:00: [Slide 1 - The kernel report]

>> JON CORBET: Hi. Thanks a lot. Good morning everybody. How many of you have seen me give one of these talks before? [Laughter] A fair number.

[Slide 2 - The plan]

Well you'll be glad to hear I've reorganised it.

The plan remains the same, which is to look back over a years worth of kernel developments with an eye towards what's going on in the future. I've changed the way things are done. Hopefully it will work out well.

[Slide 3 - Starting off 2011]

We're actually going to start just over a year ago with.. at the beginning of 2011 we saw the release of the 2.6.37 kernel.

What better to start a new year than with a new kernel? This was a fairly big release with well over 11,000 changesets in it.

This kernel brought in the first of a set of scalability patches for the virtual filesystem layer which added a fair amount to the complexity of that layer but also if you had the right kind of workload brought about something of the order of 30% performance improvement if you were doing lots of opens and closes that sort of thing. So that was good to have.

Block I/O bandwidth controller.. its actually a second bandwidth controller working at a higher level in the I/O scheduler stack allowing

6:00 - 7:00:

the placement of absolute limits on block I/O bandwidth

Finally got some support for the point to point tunnelling protocol in the mainline kernel.

Basic support for the parallel NFS protocol and

Wakeup sources which is an interesting.. on its own wakeup sources is just an accounting mechanism for tracking devices in the system that can wake the system from a sleep state but its part of a bigger effort to replicate the android opportunistic suspend mechanism and provide an implementation of that mechanism that works well within the mainline kernel. So we are still seeing pieces of that going in and pieces of it under discussion but at some point we may have a solution for that

So that was 2.6.37 - a lot went in there.

[Slide 4 - What have we done since then?]

And a lot has happened since then. So what has gone on since 2.6.37?

We've made 5 more kernel releases. I can call them out as i come to them going on the year.

We've merged almost 60,000 change sets it was over the course of the last year. These have come from over 3000 developers and at this point we have over 400 companies that we can identify that have contributed to the kernel

7:00 - 8:00:

So, I've put up numbers like this before. We've seen them before.

We know at this point that the kernel is a very active, very fast moving project. Perhaps the biggest on the planet, hard to say and it continues to move on and it shows no real signs of slowing down

[Slide 5- February]

So February of 2011

[Slide 6 - Greg K-H quote]

One of the things that happened early on in february was a little note from Greg Kroah-Hartman congratulating ralink saying as you can see ralink has stopped dumping drivers on us and instead is now working on patching the driver that we already have in the upstream kernel and trying to make that driver support their new hardware this he said shows a huge willingness to learn how to work with the kernel community and they need to be praised for this change in attitude

This is..i mean its a nice note but there is nothing all that special in a way its something that we go through with a lot of companies they take a little while to figure out how to work with us and then they do

8:00 - 9:00:

and so we see a lot of progress as companies figure out how does mainline kernel process work, how can we get our code in there, why is it in our interest to do so and then they figure how to do it and they become part of the machine. And we see this happening over and over again

[Slide 7 - Employer Contributions]

So this seems a good as time as any to put up this slide. This is a variant of a slide that i've been putting up for a while showing the top contributors to the kernel over the course of the last year from the beginning of the 2.6.38 development cycle through the 3.2 release

So, we see as always, volunteers top of the list at just under 14%. The percentage of changes coming in from people working on their own time has actually slowly fallen over the years and why that is is hard to say. One could take a pessimistic view and say that the kernel is getting too big and too complex, the easy projects are done and so we are putting off our volunteers that way. On the other hand, one could look at this and one could say well anybody who has shown any ability to actually get code into the kernel in any kind of reliable way

9:00 - 10:00:

tends not to stay a volunteer for very long unless they really really want to because they tend to get buried in job offers.

so that of course is not going to be a bad thing.

other than that we see a lot of the same companies that we've been seeing for quite a long time

we can see companies that are not only competing fiercely in other areas of the market but in fact at this point they all seem to be suing each other elsewhere [Laughter] but they are still working together quite well at this level and um.. the situation hasn't changed a whole lot

but here's one change I want to call out

this is.. was.. alright.. we'll do it the old fashioned way. no we won't..

[Slide 9 - Kernel changeset contributions by employer]

speak to me.. come on.. um.. alright. well. this is the one i was going to get to eventually. um.. what is going on here.. alright.. we'll get there

10:00 - 11:00:

never done that before

This is just a plot of the percentage contributions from the top companies. The same companies we saw on the last slide and we see.. in a noisy sort of way.. we have horizontal lines. Right? The companies who were contributing back around 2.6.20 which is when this slide starts are still contributing heavily now.

The big change I want to call out now is those two heavy lines at the bottom. Those two lines correspond to TI and Samsung. Right? And they correspond to a trend we seeing in general which is a much increased of level of involvement of the mobile and embedded community as mobile Linux grows in importance and grows in deployments these companies are figuring out that they need to work with the mainline and they are doing so.

So we're seeing this strong upward trend in contributions from that part of the market. I think we will continue to see that for quite some time

[Slide 10 - Also in February]

One other thing that happened in February, just thought I'd point out quickly,

11:00 - 12:00:

This didn't actually happen then but this when it came out and became well known. Red Hat for their enterprise kernel stopped shipping individual patches with their kernel and now you just get one big blog with all their changes. All 7699 changes in their current kernel kind of mixed in together into a single thing. So its become much harder for people who want to look in there and see what are the individual changes that Red Hat has actually made to the kernel. And why have they done that. And that's kind of a sad statement on the nature of the competition at that level of the marketplace. And there's not much to be done for it. It is of course entirely compliant with the licensing and so on but its not something that our community has really welcomed

[Slide 11 - March]

[Slide 12 - 2.6.38]

Alright.. Let's move on to March.. Well. Another month. Another kernel release. That's when 2.6.38 came out

A couple of very interesting patches that came out then. Including per-session group scheduling. This is the famous 200 line kernel patch that people were talking about for a while that turned out into about 800 line kernel patch by the time it actually went into the mainline

12:00 - 13:00:

that allows the kernel to employ the group scheduling mechanism automatically and partition processes into different groups and schedule them.. schedule the groups against each other this can give you much nicer interactivity in desktop situations. Its useful in a lot of other situations as well, to keep different groups of processes from interfering with each other in the scheduler and the nice thing about this particular patch is not that it added this feature because we've had this feature for years. It sort of made it just work. There's a whole lot of nice things that we have in the kernel that people don't really make a whole lot of use of because you have to do fiddly things with them to make them work. If you can make them simply work for people then things are a whole lot better

Transparent huge pages, which is also on the list, is another example of that. The huge page mechanism in most processors allows the memory management unit to work with much larger pages. You get a nice performance improvement out of that for just about any workload you can think of because you save a lot of pressure on your translation look aside buffer and such.

Transparent huge pages used to require you set up huge TLBFS to the side

13:00 - 14:00:

make changes to your application to make use of it and so on. So there weren't too many people actually using it. Now we're all using it because it simply works in the system and we all get the benefits from that

So we had various other things. Including the other half of the virtual file system scalability patch set I mentioned before. Transmit packet steering which is a networking scalability change that came out of Google and improvements to the block i/o bandwidth controller and of course a whole bunch of other stuff but its those two patches i think that were really the significant features of 2.6.38

[Slide 13 - Linus quote]

Something else that happened in March was that Linus threw a temper tantrum. This is not necessarily all that surprising, it happens but this was a fairly big one

He got a bunch of pull requests from ARM community and he decided that he was really just fed up with them so he stopped actually pulling them and said "ok somebody needs to get a grip in the ARM community". So, what's going on here

[Slide 14 - What is the "ARM problem"?]

14:00 - 15:00:

I probably don't need to tell the people in this room that the ARM architecture is interesting, in that it doesn't really come with the platform defintion the way some other architectures do. Every ARM system is unique in its own very special way. And so, there's a lot less commonality in terms of the code needed to support those systems

When i say the "Embedded" mindset what i mean is.. we have a lot of people working on their own special little projects working under intense time pressures and so on and so they've tended to solve their specific problem and if they put code upstream at all they've worked in their own piece of the tree and not really thought about making the kernel better for everybody involved.. so we've ended up with.. um.. with a lot of stuff.. there's really been nobody being overseeing this tree to try to make this better. so we get a lot of little sub-trees with a lot of duplicated code and a fairly big ugly mess has resulted in that tree

15:00 - 16:00:

[Slide 16 - Why is this happening]

Another way of putting this is that for years we've been asking the embedded community to contribute back to the kernel. Please please give us your code back. And the fact is that they are now doing that. Right? What we have here is a problem that is a result of our own success. We've gotten what we wished for. You should always be careful what you wish for. But in fact what is happening is really a good thing. The only real problem is that we haven't developed the processes within the community to manage all of this stuff

[Slide 17 - Cleaning up the mess]

So, what's doing.. what's happening? We're trying to clean things up. More high level oversight now. Arnd is running a tree that funnels a lot of the system on chip stuff into the kernel and so on. Trying to keep a better grip on it. There's a lot of cleanup going on at various levels. Consolidating code that was duplicated across all the various different ARM sub architectures and a move towards the device tree mechanism that can hopefully someday help us get rid of these board files and such

16:00 - 17:00:

and maybe someday i doubt we'll ever have a single kernel that runs on every ARM system but we can maybe have a kernel that runs a lot of the more popular ones without having to build it specifically for whatever system you're working on at any given time we're heading in that direction. things are getting a whole lot better

And ARM is not only becoming a proper first tier architecture its actually starting to drive things in interesting ways. If you look on LWN today we've just posted an article from an ARM developer about a concept called big dot little. We've got system on chips now that have two different classes of ARM processors on them. There's the big fast power hungry one and the little slow power efficient one and you try to figure out which one of those you should be using for any given workload at any given time. This is going to stress the scheduler in very interesting ways. The scheduler has not been written with that kind of stuff in mind so we now have stuff coming up from the mobile embedded world that is going to be driving the future directions of the core kernel and its going to be very interesting to watch

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