Solid-State Disks: Pushing the Envelope in Blade Server Design
CGL and Standard Linux Distributions
A common question from interested parties is how CGL-related requirements and enhancements affect a "standard" Linux distribution. Is it still Linux? Is the source still freely available? Where do the enhancements required for CGL registration actually come from? Providing an overview of the Linux kernel development and enhancement process provides good insights into the answers to these and related questions.
Linux is the operating system of choice for most new embedded system development projects. Embedded Linux vendors such as TimeSys produce hardware-optimized Linux distributions that are tailored to specific custom and reference embedded hardware platforms. The release of the 2.6 Linux kernel has increased the general performance and responsiveness of Linux, the number of supported processors and architectures, and the spectrum of supported buses, interfaces, and devices. 2.6-based Linux distributions are extremely stable, are available from almost every major Linux vendor, and provide substantial technical improvements over earlier versions of the Linux kernel, such as 2.4.
Parallel to mainline development efforts to increase the performance and hardware support in Linux are numerous software projects focused on improving and extending its core capabilities. The development of most of these projects takes place outside of the core kernel development line, with the hope that many of them will eventually be merged into the kernel. Whether projects are eventually merged into the kernel depends on a number of factors such as whether they are useful to the general Linux community, whether they are cleanly and "correctly" implemented, and whether they are philosophically viewed as "the right thing" to be integrated into the kernel.
The standard Linux kernel is designed to be a general-purpose, high-performance kernel with no particular bias towards the needs of any one industry, set of users, or hardware architecture. Some of the capabilities required by industry-focused specifications like CGL, such as integrated kernel debugging for serviceability purposes, may never be merged into the core kernel because of their potential impact on overall Linux performance or because there is no single, architecture-neutral solution that stands out between competing approaches to solving that particular problem.
For example, many of the capabilities required by specific industries are already available for Linux but have not yet been merged into the kernel for one reason or another. The CGL specification is a good example of this because it identifies a number of requirements in areas such as availability, serviceability, and scalability that are not currently satisfied by the vanilla Linux kernel available from www.kernel.org. This is not a deficiency in the standard Linux kernel, but a simple by-product of different focus areas.
Processor and architecture issues require special consideration when developing and supporting a Carrier Grade-registered Linux distribution. The x86 architecture and related platforms are the traditional focus area for Linux development, and many of the Open Source projects that provide the features required for CGL registration have been developed and tested only on x86 platforms. However, most telecommunications and network industry infrastructure is based around PowerPC (PPC) processors and related platforms. To serve the CGL market, vendors who are producing CGL distributions, such as TimeSys, must have historical expertise in developing Linux distributions for segments where PPC processors have also always had primary market share, such as embedded computing. Such vendors are therefore extremely familiar with architecture-specific issues associated with porting and supporting high-performance Linux on non-x86 platforms.
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