On Fri, 19 Feb 2021 19:13:09 +0000 Piscium via arch-general wrote:

On Fri, 19 Feb 2021 at 13:37, Arch Linux: Recent news updates: Giancarlo Razzolini via arch-announce wrote:

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As linux-lts moved to the 5.10 version, all official kernels of Arch Linux now support zstd compressed initramfs images, so mkinitcpio is switching to zstd compressed images by default with version 30, which is currently on [testing].

If, for any reason, you are using a kernel version prior to 5.9, make sure to change mkinitcpio.conf COMPRESSION to use one of the compressors supported, like gzip, otherwise you **will not** be able to boot images generated by mkinitcpio.

I am not sure I understand this. If someone has the default mkinitcpio.conf it won't boot?

In my case I set it to lz4 over a year ago for speed.

If someone has the default mkinitcpio.conf AND a kernel older than any Arch ships, then yes, it may not boot.

zstd is even faster at decompressing at boot than lz4 now? On Fri, Feb 19, 2021 at 1:45 PM Giancarlo Razzolini via arch-general < arch-general@lists.archlinux.org> wrote:

Em fevereiro 19, 2021 16:13 Piscium via arch-general escreveu:

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On Fri, 19 Feb 2021 at 13:37, Arch Linux: Recent news updates: Giancarlo Razzolini via arch-announce wrote:

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As linux-lts moved to the 5.10 version, all official kernels of Arch

Linux now support zstd compressed

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initramfs images, so mkinitcpio is switching to zstd compressed images by default with version 30, which is currently on [testing].

If, for any reason, you are using a kernel version prior to 5.9, make sure to change mkinitcpio.conf COMPRESSION to use one of the compressors supported, like gzip, otherwise you **will not** be able to boot images generated by mkinitcpio.

I am not sure I understand this. If someone has the default mkinitcpio.conf it won't boot?

In my case I set it to lz4 over a year ago for speed.

If you set COMPRESSION, it will use whatever you have set. If you're using lz4 now, you might want to try zstd. It's faster to generate images now.

Regards, Giancarlo Razzolini

Em fevereiro 20, 2021 2:52 mike lojkovic via arch-general escreveu:

zstd is even faster at decompressing at boot than lz4 now?

I don't think you'll notice much difference with either one. Regards, Giancarlo Razzolini

On 2/20/21 12:11 PM, Andreas Radke via arch-general wrote:

Am Sat, 20 Feb 2021 07:50:58 -0300 schrieb Giancarlo Razzolini via arch-general :

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Em fevereiro 20, 2021 2:52 mike lojkovic via arch-general escreveu:

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zstd is even faster at decompressing at boot than lz4 now?

I don't think you'll notice much difference with either one.

Regards, Giancarlo Razzolini

Depends on the system cpu power. On slow cpu systems lz4 is much faster when compressing the image and also decompressing. Though you hardly notice the decompression time difference.

On slow discs with a fast cpu a better compression may turn this around.

In many cases zstd compression gives a better compromise nowadays with a powerful enough cpu. On my older systems with fast discs but slow cpus I keep using lz4.

-Andy

I was also wondering what gives the best speed. I got a boot partition with 250mb, wouldn't it make sense to use CAT aka no compression? Or is that also slower? I mean the kernel should fit into that large space, it is allocated anyways, right? ~Nico

What about when you have an nvme disc with relatively slow boot up times? On Sat, Feb 20, 2021 at 10:20 AM Jonathon Fernyhough via arch-general < arch-general@lists.archlinux.org> wrote:

On 20/02/2021 16:17, NicoHood via arch-general wrote:

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I was also wondering what gives the best speed. I got a boot partition with 250mb, wouldn't it make sense to use CAT aka no compression?

It's a balance between CPU usage and disk IO. cat requires more data to be read from disk, zstd requires more CPU time.

Slow CPU and fast SSD? cat. Fast CPU and slow HDD? zstd.

On Sat, Feb 20, 2021 at 19:33:26 +0100, Geert Hendrickx via arch-general wrote:

I benchmarked it on my mkinitcpio image, and zstd with mkinitcpio's default compression level 19 (standard COMPRESSION_OPTIONS for zstd) is several orders of magnitude slower than lz4, only to gain ~30% extra compression. It is slower to decompress too, but less noticeably so.

Sorry, just noticed the default -19 flag was dropped in mkinitcpio v30. zstd compression/decompression speed is much better now, comparable to gzip but with smaller compressed files. (lz4 is still faster but gives bigger files.) Geert

On Sat, Feb 20, 2021 at 21:25:21 +0100, mpan via arch-general wrote:

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I benchmarked it on my mkinitcpio image, and zstd with mkinitcpio's […] Though you have benchmarked a wrong thing. It’s decompression time that matters here, not compression. The image is compressed to make it load faster during boot and that’s the important metric here.

Compression time matters also, since on many systems an initramfs gets booted only once or a few times for every time one gets generated, and zstd -19 is ridiculously slow for larger files, However mkinitcpio v30 reverted to zstd's default compression level 3, which is much better. It's a different tradeoff for, say, a package that gets built once and downloaded thousands of times, for which bandwidth savings outweigh the compression overhead. Geert

Those milliseconds matter. When you have a thousand processes starting up shaving off a couple fractions of a second on each helps you hit the less than 10 second boot time. On Sun, Feb 21, 2021 at 4:48 AM Archange via arch-general < arch-general@lists.archlinux.org> wrote:

Le 21/02/2021 à 02:56, Geert Hendrickx via arch-general a écrit :

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On Sat, Feb 20, 2021 at 21:25:21 +0100, mpan via arch-general wrote:

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I benchmarked it on my mkinitcpio image, and zstd with mkinitcpio's […] Though you have benchmarked a wrong thing. It’s decompression time that matters here, not compression. The image is compressed to make it load faster during boot and that’s the important metric here.

Compression time matters also, since on many systems an initramfs gets booted only once or a few times for every time one gets generated, and zstd -19 is ridiculously slow for larger files, However mkinitcpio v30 reverted to zstd's default compression level 3, which is much better.

Excepted that decompression is a blocking event for boot, while compression is async.

Anyway, based on the benchmark published on the PR that reverted to the default level, using -8 seems the best tradeoff for fast compression and small size, and −18 if space really is an issue (or you’re reading the file from a floppy…).

Also, on most systems nowadays we are talking about changes in the order of hundreds of milliseconds, while I take ~5s to type my entire LUKS passphrase on boot. So…

On 2021-02-21 20:17:28, Archange via arch-general wrote:

Well I don’t boot often enough for even say 30s to make a difference (and my boot time is actually dominated by 1. UEFI and 2. Passphrase input). Outside of being impressive, what does a <10s boot time actually achieves? It likely takes you more time to adopt a good posture in front of your computer while it is booting up. If we were talking 10s vs 2 min I’d understand, but we are barely talking 20s vs 10s…

I can provide a bit of a counterpoint to this. I always boot and shut down my laptop, so boot time has an effect on me! Passphrase input is also the main slowdown, along with UEFI. I'm not always looking to reduce boot times, but any imporovements are always welcomed.

Do I have to wait for kernel 5.11 in order to use zstd? On 2/19/21 2:13 PM, Piscium via arch-general wrote:

On Fri, 19 Feb 2021 at 13:37, Arch Linux: Recent news updates: Giancarlo Razzolini via arch-announce wrote:

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As linux-lts moved to the 5.10 version, all official kernels of Arch Linux now support zstd compressed initramfs images, so mkinitcpio is switching to zstd compressed images by default with version 30, which is currently on [testing].

If, for any reason, you are using a kernel version prior to 5.9, make sure to change mkinitcpio.conf COMPRESSION to use one of the compressors supported, like gzip, otherwise you **will not** be able to boot images generated by mkinitcpio. I am not sure I understand this. If someone has the default mkinitcpio.conf it won't boot?

In my case I set it to lz4 over a year ago for speed.

Em fevereiro 22, 2021 10:23 JustKidding via arch-general escreveu:

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Do I have to wait for kernel 5.11 in order to use zstd?

No, zstd is supported since kernel 5.9.

The unfortunate consequence of this is that currently Arch only has 5.10 kernels available, and a mkinitcpio that by default only works with >5.9. But people on Haswell CPUs had to have 5.4 pinned, since any later kernel was crashing the GPU, so the mkinitcpio change will break their boot unless they are extra/doubly careful. -- damjan

Le 22/02/2021 à 05:12, Kevin Morris via arch-general a écrit :

A 10 second improvement is _large_. You may think that you don't need it because you're sitting at your computer, but think about servers, vms, automated systems... Every second makes things quicker. Moving from 20 seconds to 10 seconds is halving its boot time.

That is a good thing.

Right, that is much more relevant indeed. Though my dedicated server are spending ~1min in BIOS, so my kernel actually booting in 3s on them is rather… pointless. ^^ But I understand that VPS/VMs are a different thing though. ;)