A report from the first Korea Linux Forum

Some years ago, the Open Source Development Laboratories recognized that Japanese companies were increasingly making use of Linux but were not always participating in the development community. To help close the loop, OSDL began a series of events where Japanese developers could hear from — and talk with — developers from the wider community; that practice continued into the Linux Foundation era. Your editor was lucky enough to be able to attend a number of these events, starting in 2007. These conferences cannot claim all of the credit for the marked increase in contributions from Japan over the last several years, but it seems clear that they helped. The Japanese Linux Symposium has since transformed into LinuxCon Japan, a proper development conference in its own right.

KLF is clearly meant to follow the same pattern, but there is a big difference this time around: community participation from Korea is already significant and increasing in a big way. For example, Samsung first appeared in the list of top kernel contributors in the 2.6.35 development cycle over two years ago; it has held its place on that list ever since. Contributions from Korean developers are clearly not in short supply. That made the job of the KLF speakers easy; rather than encouraging Korean developers to participate more, they were able to offer their thanks and talk more about how to get things done in the community.

The first talk (after the inevitable cheerleading session by Linux Foundation head Jim Zemlin) was by Samsung vice president Wonjoo Park; his goal was to make it clear that Linux is an important resource for Samsung, the "host sponsor" for the event as a whole. Software, he said, is the means for product differentiation in today's market; it is the most important part of any product and drives the business as a whole. Samsung, it seems, is a software company.

The company got its start with Linux in 2003, using a distribution from MontaVista. Use of Linux expanded over the years: appliances in 2005, televisions in 2006, and so on. Samsung's first Linux smartphone came out in 2004; it featured a voice-activated phone book. In 2007 Samsung joined LiMo; the first LiMo-based phone came out in 2009. In 2012, products all across the Samsung line, from phones and tablets to home theater systems, cameras and printers, are all based on Linux.

Now, of course, much of the company's efforts are going into furthering the Tizen distribution. He mentioned the recently-posted F2FS filesystem: Samsung could have held onto that code and kept F2FS proprietary, he said, but that would have deterred innovation; sharing it, instead, allows the company to accept changes from others. Samsung has also put together an extensive license compliance process after a "rough start" that forced the company to apologize to the community. One of the results is opensource.samsung.com, one-stop shopping for the source code for Samsung's products.

In summary, he said, Linux has become a "core competitive competence" for Samsung; the company would not be able to do what it does without it.

Korean rockstar hacker Tejun Heo gave a well-received keynote presentation on what it is like to be a community developer. It is hard, he said, but then, working in Korean companies, where the expectations are high, is hard in general. Developers who can succeed in the corporate setting can make it in the community as well. Developing in the community has a lot of rewards, including the fact that credit for the work stays with the developer rather than accruing to the sponsoring company. It is a challenging path, but full of benefits.

KLF was, like the early Japan events, oriented toward information delivery rather than the sort of critical discussion of ongoing work that one finds at a serious development conference. That does not mean that there was no development work on display, though. Arguably the most interesting talk was Kisoo Yu's discussion of the big.LITTLE switcher (originally written by Nicolas Pitre). Big.LITTLE is an ARM-based system-on-chip architecture that combines a number of slow, power-efficient processors with fast, power-hungry processors on the same chip. In this particular case, Kisoo discussed an upcoming Samsung Exynos processor combining four Cortex A7 processors with four Cortex A15's — yes, an eight-core SoC.

Big.LITTLE poses a number of interesting challenges for the kernel: how does one schedule tasks across the system to optimize both throughput and power consumption? Kisoo described two approaches, the first of which involves running Linux under a simple hypervisor that transparently switches the hardware from slow mode (running on all four A7's) to fast mode (all four A15's) without the kernel's participation or awareness. The alternative approach has the kernel itself explicitly managing the SoC as a four-processor system, switching each one independently between the fast and slow cores as if it were simply adjusting the CPU's clock frequency. Either way, a number of heuristics have been developed to try to determine the best time to make the switch from one to the other. This SoC offers an interesting hardware feature that can quickly transfer interesting L2 cache entries from one core to another to speed the switching process, which can be done in 30µs or so.

Perhaps the most interesting takeaway from the talk is that we still don't really have a good idea for how to manage these systems. This SoC is a true eight-core processor; it would seem that an optimal approach would manage it as such rather than as a four-core system with a big "turbo" button. The fact that we are, thus far, unable to do so is not an indictment of the developers working on the task in any way; it is clearly a hard problem without much in the way of useful solutions in the literature. As is the case with many other hard operating system problems, the work being done now will get us closer to an understanding of the issues and the eventual development of better solutions.

One thing that became clear at the inaugural KLF is that Korea is increasingly supplying a lot of sharp minds ready to work on problems like this, and that this trend looks set to continue indefinitely. Energy abounds, as does, seemingly, a good sense of fun. Your editor would like to thank our hosts in Korea for hosting an engaging event, treating us so well, and even for inflicting "Gangnam style" K-pop music on us at the conference dinner. And, of course, thanks are due to the Linux Foundation for supporting your editor's travel to the event.