@cborntra v5.13 ubuntu kernel's s390 configuration with zstd -22 --ultra compression is 8.5 MB, whereas gzip -9 is 11M.
Thus for gzip to win at bootspeed the decompression speed has to compensate for 2.5M of i/o and be faster than zstd. Unaccelerated decompression comparison still gives me faster decompression with less i/o with zstd compressed kernel image. At Canonical we still do not have z15 mainframe available for us to benchmark this. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1931725 Title: initramfs-tools & kernel: use zstd as the default compression method Status in Ubuntu on IBM z Systems: New Status in initramfs-tools package in Ubuntu: Fix Released Status in linux package in Ubuntu: New Bug description: Turns out that loading is always the slow part in loading initramfs into memory and decompressing it since decompression is always the final 10-20% or so of the task. It therefore makes sense to use a good compressor that shrinks the initramfs as much as possible with little decompression overhead. Benchmarking zstd vs lz4 shows that while zstd can be ~5x slower in decompression, the image size is much smaller with zstd than lz4, and since ~80-90% of the boot time is loading the image it makes sense to use zstd. Attached is a libreoffice spread sheet showing typical load and decompression times for a fairly standard 3.4 GHZ intel box with data for load times for a 5400 RPM, 7200 RPM and SATA SSD drives. The conclusions from the test results (attached) show: 1. Loading time is always significantly slower than decompression time. 2. ZSTD is 5x slower than LZ4 in decompression speed but produces far better compressed images 3. Given that loading time is the major factor in loading + decompression, ZSTD is best for kernel and initramfs boot timings. (Also refer to https://kernel.ubuntu.com/~cking/boot-speed-eoan-5.3 /kernel-compression-method.txt for some raw data on drive load speeds for the same UEFI box I did a couple of years ago). amd64 supports zstd, but s390x does not. Will use this bug to enable zstd support on s390x. Upstream submitted patch https://lore.kernel.org/linux-s390/20210615114150.325080-1-dimitri.led...@canonical.com/T/#u To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-z-systems/+bug/1931725/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
