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Kernel images are often stored compressed because they can take up a significant amount of disk space. One of the popular formats for this is LZ4. Even though it does not offer the best compression ratio, it excels at decompression speeds. On arm64, kernels do not come with their own decompressor like they do on x86. Instead, it is the job of the bootloader to decompress the kernel before it is executed. To this end, add crosvm support for LZ4 decompression of kernel images, via the Rust-safe lz4_flex library. LZ4 file format is detected automatically via one of its magic numbers. Otherwise crosvm will fall back to loading the kernel as a raw image. Some rough numbers using Android's Generic Kernel Image on Pixel 8: * compresion rate: 49% (33MB -> 16MB) * decompression time: 20-30ms Given that the total VM boot takes about 1.5s, the overhead is more than acceptable. BUG=b:315141974 TEST=tools/dev_container tools/run_tests --platform=aarch64 Change-Id: I1030abe6fdf7087603cea9ac5273bf9136bad693 Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/5110323 Reviewed-by: Daniel Verkamp <dverkamp@chromium.org> Reviewed-by: Dennis Kempin <denniskempin@google.com> Commit-Queue: David Brazdil <dbrazdil@google.com> |
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