From ea7ff37c6b44dc4db29604f94ad9ce088c798c4c Mon Sep 17 00:00:00 2001 From: Matthias Schiffer Date: Wed, 13 May 2020 20:33:46 +0200 Subject: [PATCH] build: compress kernel debuginfo using zstd 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 (cherry picked from commit 4bd7990488b0ca7b5cae16f0a9147a4146759053) --- include/kernel-build.mk | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/kernel-build.mk b/include/kernel-build.mk index 3fdf7efc52..af7c3a8f0b 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