From 7472ff8adad8655f38b060a602f66e59c93c4793 Mon Sep 17 00:00:00 2001 From: Lasse Collin Date: Sun, 21 Jul 2024 16:36:29 +0300 Subject: xz: adjust arch-specific options for better kernel compression Use LZMA2 options that match the arch-specific alignment of instructions. This change reduces compressed kernel size 0-2 % depending on the arch. On 1-byte-aligned x86 it makes no difference and on 4-byte-aligned archs it helps the most. Use the ARM-Thumb filter for ARM-Thumb2 kernels. This reduces compressed kernel size about 5 %.[1] Previously such kernels were compressed using the ARM filter which didn't do anything useful with ARM-Thumb2 code. Add BCJ filter support for ARM64 and RISC-V. Compared to unfiltered XZ or plain LZMA, the compressed kernel size is reduced about 5 % on ARM64 and 7 % on RISC-V. A new enough version of the xz tool is required: 5.4.0 for ARM64 and 5.6.0 for RISC-V. With an old xz version, a message is printed to standard error and the kernel is compressed without the filter. Update lib/decompress_unxz.c to match the changes to xz_wrap.sh. Update the CONFIG_KERNEL_XZ help text in init/Kconfig: - Add the RISC-V and ARM64 filters. - Clarify that the PowerPC filter is for big endian only. - Omit IA-64. Link: https://lore.kernel.org/lkml/1637379771-39449-1-git-send-email-zhongjubin@huawei.com/ [1] Link: https://lkml.kernel.org/r/20240721133633.47721-15-lasse.collin@tukaani.org Signed-off-by: Lasse Collin Reviewed-by: Sam James Cc: Simon Glass Cc: Catalin Marinas Cc: Will Deacon Cc: Paul Walmsley Cc: Palmer Dabbelt Cc: Albert Ou Cc: Jubin Zhong Cc: Jules Maselbas Cc: Emil Renner Berthing Cc: Greg Kroah-Hartman Cc: Herbert Xu Cc: Joel Stanley Cc: Jonathan Corbet Cc: Krzysztof Kozlowski Cc: Michael Ellerman Cc: Randy Dunlap Cc: Rui Li Cc: Thomas Gleixner Signed-off-by: Andrew Morton --- init/Kconfig | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'init') diff --git a/init/Kconfig b/init/Kconfig index 5783a0b87517..583cb07176a9 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -310,8 +310,9 @@ config KERNEL_XZ BCJ filters which can improve compression ratio of executable code. The size of the kernel is about 30% smaller with XZ in comparison to gzip. On architectures for which there is a BCJ - filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ - will create a few percent smaller kernel than plain LZMA. + filter (i386, x86_64, ARM, ARM64, RISC-V, big endian PowerPC, + and SPARC), XZ will create a few percent smaller kernel than + plain LZMA. The speed is about the same as with LZMA: The decompression speed of XZ is better than that of bzip2 but worse than gzip -- cgit v1.2.3