Re: [PATCH] x86/boot: Support uncompressed kernel

[Michal Marek]

On 2017-03-23 13:51, Chao Peng wrote:
> Compressed kernel has its own drawback: uncompressing takes time. Even
> though the time is short enough to ignore for most cases but for cases that
> time is critical this is still a big number. In our on-going optimization
> for kernel boot time, the measured overall kernel boot time is ~90ms while
> the uncompressing takes ~50ms with gzip.
> 
> The patch adds a 'CONFIG_KERNEL_RAW' configure choice so the built binary
> can have no uncompressing at all. The experiment shows:
> 
>     kernel               kernel size    time in decompress_kernel
>     compressed (gzip)    3.3M           53ms
>     uncompressed         14M            3ms
> 
> Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/boot/compressed/Makefile |  3 +++
>  arch/x86/boot/compressed/misc.c   | 14 ++++++++++++++
>  init/Kconfig                      |  7 +++++++
>  scripts/Makefile.lib              |  8 ++++++++
>  4 files changed, 32 insertions(+)
> 
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index f9ce75d..fc0e1c0 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -73,6 +73,8 @@ $(obj)/vmlinux.relocs: vmlinux FORCE
>  vmlinux.bin.all-y := $(obj)/vmlinux.bin
>  vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += $(obj)/vmlinux.relocs
>  
> +$(obj)/vmlinux.bin.raw: $(vmlinux.bin.all-y) FORCE
> +	$(call if_changed,raw)
>  $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE
>  	$(call if_changed,gzip)
>  $(obj)/vmlinux.bin.bz2: $(vmlinux.bin.all-y) FORCE
> @@ -86,6 +88,7 @@ $(obj)/vmlinux.bin.lzo: $(vmlinux.bin.all-y) FORCE
>  $(obj)/vmlinux.bin.lz4: $(vmlinux.bin.all-y) FORCE
>  	$(call if_changed,lz4)
>  
> +suffix-$(CONFIG_KERNEL_RAW)	:= raw
>  suffix-$(CONFIG_KERNEL_GZIP)	:= gz
>  suffix-$(CONFIG_KERNEL_BZIP2)	:= bz2
>  suffix-$(CONFIG_KERNEL_LZMA)	:= lzma
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index 79dac17..fb3cd43 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -123,6 +123,20 @@ static char *vidmem;
>  static int vidport;
>  static int lines, cols;
>  
> +#ifdef CONFIG_KERNEL_RAW
> +#include <linux/decompress/mm.h>
> +static int __decompress(unsigned char *buf, long len,
> +			long (*fill)(void*, unsigned long),
> +			long (*flush)(void*, unsigned long),
> +			unsigned char *outbuf, long olen,
> +			long *pos,
> +			void (*error)(char *x))
> +{
> +	memcpy(outbuf, buf, olen);
> +	return 0;
> +}
> +#endif
> +
>  #ifdef CONFIG_KERNEL_GZIP
>  #include "../../../../lib/decompress_inflate.c"
>  #endif
> diff --git a/init/Kconfig b/init/Kconfig
> index 2232080..1db2ea2 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -137,6 +137,13 @@ choice
>  
>  	  If in doubt, select 'gzip'
>  
> +config KERNEL_RAW
> +	bool "RAW"
> +	help
> +	  No compression. It creates much bigger kernel and uses much more
> +	  space (disk/memory) than other choices. It can be useful when
> +	  decompression speed is the most concern while space is not a problem.

This needs to depend on a HAVE_KERNEL_RAW config that is selected by the
architectures that implement this target (x86).

Michal