On 1/22/25 16:08, Jann Horn wrote:
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?
Hi Jann,
Yes, different algos have different ways of specifying compression
levels. You cannot have one single option for all of the available
compressors.
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.
Here is my take for zstd which I've been using for a while now.
(zstd levels above 19 need the '--ultra' switch, hence the honkytonk below).
--
From 2e9a0e058e10a428d2ee079b969627e475cc0f2e Mon Sep 17 00:00:00 2001
From: Tor Vic <torvic9@xxxxxxxxxxx>
Date: Tue, 6 Aug 2024 11:24:32 +0200
Subject: [PATCH] Kbuild, zstd: Allow users to choose a compression level for
the kernel image
Signed-off-by: Tor Vic <torvic9@xxxxxxxxxxx>
---
init/Kconfig | 13 +++++++++++++
scripts/Makefile.lib | 9 ++++++++-
2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/init/Kconfig b/init/Kconfig
index 105cdd05db759..9c39bc17964de 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -380,6 +380,19 @@ config KERNEL_UNCOMPRESSED
endchoice
+menu "ZSTD compression options"
+ depends on KERNEL_ZSTD
+
+config ZSTD_COMPRESSION_LVL
+ int "Compression level (1-22)"
+ range 1 22
+ default "22"
+ help
+ Choose a compression level for zstd kernel compression.
+ Default is 22, which is the maximum.
+
+endmenu
+
config DEFAULT_INIT
string "Default init path"
default ""
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 7395200538da8..58884363ebc62 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -516,6 +516,13 @@ quiet_cmd_xzmisc = XZMISC $@
# decompression is used, like initramfs decompression, zstd22 should
likely not
# be used because it would require zstd to allocate a 128 MB buffer.
+ifdef CONFIG_ZSTD_COMPRESSION_LVL
+zstd_comp_lvl := $(CONFIG_ZSTD_COMPRESSION_LVL)
+ifeq ($(call test-gt, $(zstd_comp_lvl), 19),y)
+zstd_comp_lvl += --ultra
+endif
+endif
+
quiet_cmd_zstd = ZSTD $@
cmd_zstd = cat $(real-prereqs) | $(ZSTD) -19 > $@
@@ -523,7 +530,7 @@ quiet_cmd_zstd22 = ZSTD22 $@
cmd_zstd22 = cat $(real-prereqs) | $(ZSTD) -22 --ultra > $@
quiet_cmd_zstd22_with_size = ZSTD22 $@
- cmd_zstd22_with_size = { cat $(real-prereqs) | $(ZSTD) -22
--ultra; $(size_append); } > $@
+ cmd_zstd22_with_size = { cat $(real-prereqs) | $(ZSTD) -T0
-$(zstd_comp_lvl); $(size_append); } > $@
# ASM offsets
#
---------------------------------------------------------------------------
--
