zstd with its default settings (compression level -3) compresses better
than bzip2 -9 (which is the default setting), and is an order of magnitude
faster.
I made the following measurements for the most common compression tools
(all standard Debian Buster versions, default flags unless noted
otherwise), using the debug information of a large x86-64 kernel with
ALL_KMODS:
* kernel-debug.tar: 376M
* kernel-debug.tar.gz: 101M, compressed in ~12s
* kernel-debug.tar.bz2: 91M, compressed in ~15s
* kernel-debug.tar.xz: 57M, compressed in ~101s
* kernel-debug.tar.zst: 86M, compressed in ~1s
With zstd, there is still some room for improvement by increasing the
compression, but the slight increase in compression ratio
(22.83% -> 19.46%) does not justify the significant increase in
compression time (about 5 times on my machine) in my opinion.
Note that multithreaded compression (-T argument) does not affect
reproducibility with zstd.
Signed-off-by: Matthias Schiffer <mschif...@universe-factory.net>
---
include/kernel-build.mk | 2 +-
tools/Makefile | 1 +
2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/kernel-build.mk b/include/kernel-build.mk
index c371e78ab9b0..32c91a5b8359 100644
--- a/include/kernel-build.mk
+++ b/include/kernel-build.mk
@@ -70,7 +70,7 @@ ifdef CONFIG_COLLECT_KERNEL_DEBUG
$(FIND) $(KERNEL_BUILD_DIR)/debug -type f | $(XARGS)
$(KERNEL_CROSS)strip --only-keep-debug
$(TAR) c -C $(KERNEL_BUILD_DIR) debug \
$(if $(SOURCE_DATE_EPOCH),--mtime="@$(SOURCE_DATE_EPOCH)") \
- | bzip2 -c -9 > $(BIN_DIR)/kernel-debug.tar.bz2
+ | zstd -T0 -f -o $(BIN_DIR)/kernel-debug.tar.zst
endef
endif
diff --git a/tools/Makefile b/tools/Makefile
index 02556d4b83f3..169f36c5bb69 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -37,6 +37,7 @@ tools-y += lzma squashfskit4 zip
tools-$(BUILD_B43_TOOLS) += b43-tools
tools-$(BUILD_ISL) += isl
tools-$(CONFIG_USE_SPARSE) += sparse
+tools-$(CONFIG_COLLECT_KERNEL_DEBUG) += zstd
tools-$(CONFIG_TARGET_apm821xx)$(CONFIG_TARGET_gemini) += genext2fs
tools-$(CONFIG_TARGET_tegra) += cbootimage cbootimage-configs
--
2.26.2
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