linux 2.4 or 2.6 Kernels for embedded system

Using the 2.6 kernel on embedded systems implicates the following disadvantages:

* Slow to build: 2.6 takes 30...40% longer to compile
* Big memory footprint in flash: the 2.6 compressed kernel image is 30...40% bigger
* Big memory footprint in RAM: the 2.6 kernel needs 30...40% more RAM; the available RAM size for applications is 700kB smaller
* Slow to boot: 2.6 takes 5...15% longer to boot into multi-user mode
* Slow to run: context switches up to 96% slower, local communication latencies up to 80% slower, file system latencies up to 76 slower, local communication bandwidth less than 50% in some cases.

上面的内容是从

 

2.6 focus on high end(server) performance, many feature added into 2.6 newly, can not benefit---in fact I believe it will decrease, low-end performance(such as PC, needless to say embedded environment).

The comment from denx is basically right. Typical 2.4 kernel on an
embedded platform is 600KB, might be well reduced to 500KB if
modified carefully, while the 2.6 kernel usually costs 800KB minimum. There're patches called tiny-linux which targets at a small kernel, though still not enough.

The increased memory footprint is obvious if you watch the /proc/meminfo right after bootup (before launching any application).

A most attractive feature to embedded development in 2.6 might be
its premptible kernel, which will improve the real-time characteristics to some extent but still not enough.

The block device might perform well enough in 2.6, and the file-system will usually benefit, but it's not that important to an embedded system thatn to an high-load web server.

There's still a long way for 2.6 in embedded application.

----------------------------------------------

简要地介绍一下Linux内核2.6所做的改进及新增功能
Linux2.6主要在以下的10个方面作了很大的改进，简单概括如下，有关详细情况，请参阅相关资料。
1）通过改善并行处理能力和采用POSIX线程等，提高了系统的处理能力，从而Linux真正具备大型信息系统所要求性能。
2）通过改善文件系统的输出/输入能力和提高对大容量内存的利用效率，使得Linux能够更胜任大型信息系统中的数据处理。
3）加强了对数据库应用程序的支持。
4）提高了抗系统高负荷时能力。
5）提高了系统的可用性，包括对不停机时备份和不停机时更换硬件功能的支持。
6）强化了对网络的支持，增加了对Ipv6, SCTP, IPSec，等的支持。
7）通过增加访问控制和内核暗号化技术，提高了系统的安全性。
8）强化了对电源的管理。
9）强化了对嵌入式CPU和系统的支持。
10）添加了更多的硬件驱动程序。