Allow choosing the LZ4 compression level using the new config flag CONFIG_LZ4_LEVEL. This will allow developers who want to quickly iterate with one-off kernel builds to speed up kernel compression at the cost of creating a larger kernel image. LZ4 at level 9 (which the kernel uses by default) takes ~2.8 seconds to compress a 110M large vmlinux.bin on my machine; LZ4 at level 1 just needs ~220ms wall clock time. Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> --- My patch provides kconfig for choosing compression level of LZ4; Tor Vic mentioned using kconfig for choosing the compression level of ZSTD. Does my current approach of having a kconfig option specifically for LZ4 compression level look good (and we can add the same for ZSTD later if necessary); or should there be a single kconfig option that sets a compression level that is used across all compression algorithms? I guess doing it separately for different algorithms makes more sense because different compression levels might mean different things for different algorithms? Do I need to somehow make it explicit that cmd_lz4 and cmd_lz4_with_size rely on CONFIG_LZ4_LEVEL, or does the build system figure that out on its own somehow? Experimentally it seems like the build system triggers a rebuild when the config option changes, but I'm not sure how that actually works. --- Changes in v2: - removed x86/EFI subsystems from recipients since I'm no longer touching those - rewrote patch to make LZ4 level configurable instead of offering uncompressed builds on x86 (Ard) - Link to v1: https://lore.kernel.org/r/20250121-kernel-compress-fast-v1-1-fa693b6167d4@xxxxxxxxxx --- init/Kconfig | 16 ++++++++++++++++ scripts/Makefile.lib | 4 ++-- 2 files changed, 18 insertions(+), 2 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index a20e6efd3f0fbdd7f0df2448854cc30734a0ee4f..3fd93bbe98390997e7e2d41426241b90d3b33053 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -358,6 +358,9 @@ config KERNEL_LZ4 is about 8% bigger than LZO. But the decompression speed is faster than LZO. + If you are working on the kernel and recompiling frequently, you can + adjust the compression level with CONFIG_LZ4_LEVEL. + config KERNEL_ZSTD bool "ZSTD" depends on HAVE_KERNEL_ZSTD @@ -380,6 +383,19 @@ config KERNEL_UNCOMPRESSED endchoice +config LZ4_LEVEL + int "LZ4 compression level" + range 1 12 + depends on KERNEL_LZ4 + default 9 + help + This option controls the compression level used for LZ4 invocations, + in particular for compressing the kernel image. + + If you are working on the kernel and recompiling frequently, you can + set this to a low value like 1 to speed up kernel builds at the cost + of using more disk space. + config DEFAULT_INIT string "Default init path" default "" diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 7395200538da89a2f6e6d21f8959f3f60d291d79..c3eedbc4acf133d5f9e7f13d637af09ad1968930 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -425,10 +425,10 @@ quiet_cmd_lzo_with_size = LZO $@ cmd_lzo_with_size = { cat $(real-prereqs) | $(KLZOP) -9; $(size_append); } > $@ quiet_cmd_lz4 = LZ4 $@ - cmd_lz4 = cat $(real-prereqs) | $(LZ4) -l -9 - - > $@ + cmd_lz4 = cat $(real-prereqs) | $(LZ4) -l -$(CONFIG_LZ4_LEVEL) - - > $@ quiet_cmd_lz4_with_size = LZ4 $@ - cmd_lz4_with_size = { cat $(real-prereqs) | $(LZ4) -l -9 - -; \ + cmd_lz4_with_size = { cat $(real-prereqs) | $(LZ4) -l -$(CONFIG_LZ4_LEVEL) - -; \ $(size_append); } > $@ # U-Boot mkimage --- base-commit: 95ec54a420b8f445e04a7ca0ea8deb72c51fe1d3 change-id: 20250121-kernel-compress-fast-350ce5801c28 -- Jann Horn <jannh@xxxxxxxxxx>
