Replace Real-Time OS! The advent of Linux with Priority Inheritance

[Journal reports] The World's Largest embedded Linux package publisher, American MontaVista software company, recently successfully developed a mutex Program (mutex) that includes the Priority Inheritance function) the Linux kernel is embedded to improve the response performance. The maximum response time of a common Linux kernel is about 100 ms, and the Linux kernel developed this time implements dozens of μs. The maximum response time of a common Real-Time OS is several μs, that is, the response performance has been improved to a level that can compete with the real-time OS. Kevin Morgan, vice president of technology at the company, confidently said: "This is expected to replace real-time OS. In the field of embedding, there is no field where Linux cannot meet your needs ."

Currently, most embedded Linux systems use the preemptive kernel that can switch tasks midway through the kernel execution path. After a preemptible kernel is used, the average response performance can be reduced to less than 1/10 compared to a common Linux kernel that does not use this kernel. However, it has no effect on shortening the maximum response time. Therefore, Linux cannot be used in terms of communication control purposes with short response performance requirements.

Use mutex programs to replace spin locks

The Linux kernel developed this time uses mutex programs with priority inheritance to replace the spin locks used in the previous preemptive kernel to protect the critical section, shortening the longest response time. Mutex is a common feature of General Real-Time OS such as μitron. It is a technology that will be considered to improve the Linux response performance. "After a mutex program with the priority inheritance function is added, the disadvantage is that programs with priority determination by thread lock will generate overhead," Morgan of MontaVista said. Therefore, mutex programs have never been used in the past ." If it is a spin lock, you only need to wait for the task, so the application is more concise than the mutex program.

Cancels Real-Time OS of mobile phones and supports multiple kernels

The objective of MontaVista is to apply the Linux kernel developed this time to mobile phones. The vast majority of existing mobile phones use Baseband Processing Chips and application processors to run different operating systems separately. Because the baseband processing chip for call control through communication with the base station requires a short response time, Linux in the past cannot meet the requirements. For example, for Linux-based NEC mobile phones, Linux is currently running on the application processor, while the baseband processing chip is running on μitron.

If you can run the developed Linux kernel with the priority inheritance function on the application processor, you may be able to hand over the call control processing performed by the baseband processing chip to the application processor. In this way, you can cancel the existing real-time OS. As OS only has one type of Linux, It is expected not only to improve development efficiency, but also to reduce the production cost of mobile phones by eliminating the need for Baseband Processing Chips ." (Morgan) In addition, because the Linux kernel developed this time also supports symmetric multi-processor architecture (SMP), if you use a multi-core application processor, you can maintain the overall processing performance, eliminate the need for Baseband Processing Chips.

For the Linux kernel developed this time, the company is ready to open source code to attract developers to join the Development Group so that they can continue to improve it in the future. Click here for the website of this plan. In addition, the US Timesys company is also developing a Linux kernel with the same response performance as the Linux kernel. However, "It is not open source code, and we hope to highlight its own characteristics ." (Morgan of MontaVista) (Reporter: jinteng smart technology)

From: Nikkei BP Network