Android 9 auto kernel compression

[amit251291]

Dear team,

We are working on imx8qm-mek platform running on Android 9 automotive. I was going through menuconfig and i found that none of the compression methods are enabled :

HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4

I checked these configs and i found (n) to each of them. 

What does this mean ? 

How can change compression method ?

How can i use decompressed kernel instead of compressed one ?

Is it good idea to use decompressed kernel for boot time optimization ?

Request you to provide some light here. 

[Bio_TICFSL · Accepted solution]

Hello Amit,

Although there is the popular misconception that the bz prefix means that bzip2 compression is used [...], says the opposite of your theory: the bz in bzImage has no relation to bzip2, and bzImage doesn’t have to be compressed with bzip2. In fact, the kernel’s default compression mode is still gzip, and there is little reason to use bzip2 nowadays — it is slower than LZMA and xz but doesn’t compress as well.

However This mean you can change the compressed method but we have not tested. you must use the compressed one.

Regards

[amit251291]

Thank you Bio_TICFSL‌ for the explanation. I will check this out.