日期：2015年10月7日

Linux kernel 笔记 （27）——“make clean”和“make mrproper”的区别

参考Recompiling the kernel：

Sometimes, you’ll change things so much that make can’t figure out how to recompile the files correctly. make clean will remove all the object and kernel object files (ending in .o and .ko) and a few other things. make mrproper will do everything make clean does, plus remove your config file, the dependency files, and everything else that make config creates. Be sure to save your config file in another file before running make mrproper. Afterwards, copy the config file back to .config and start over, beginning at make menuconfig. A make mrproper will often fix strange kernel crashes that make no sense and strange compilation errors that make no sense.

make clean删除object和kernel object文件，还有其它一些文件。make mrproper是make clean的超集，它还会删除config文件，依赖文件，以及其它make config生成的文件。

 

Linux kernel 笔记 （26）——利用“make -j”提高编译`kernel`速度

首先看一下-j选项在make命令中的含义：

-j [jobs], --jobs[=jobs]
        Specifies the number of jobs (commands) to run simultaneously.   If  there  is  more  than  one  -j
        option,  the  last  one is effective.  If the -j option is given without an argument, make will not
        limit the number of jobs that can run simultaneously.

也就是-j指定并行工作的job数量，例如make -j4。如果-j选项后面没有参数，则不会限制job数。

再参考《Linux kernel development》:

By default, make spawns only a single job because Makefiles all too often have incorrect dependency information.With incorrect dependencies, multiple jobs can step on each other’s toes, resulting in errors in the build process.The kernel’s Makefiles have correct dependency information, so spawning multiple jobs does not result in failures.To build the kernel with multiple make jobs, use

$ make -jn

Here, n is the number of jobs to spawn. Usual practice is to spawn one or two jobs per processor. For example, on a 16-core machine, you might do

$ make -j32 > /dev/null

可以看到指定job数是系统core数量2倍是一种推荐的做法。