Reducing initramfs size and speed up the generation

[Julian Andres Klode]

On Tue, Jul 11, 2023 at 12:53:00AM +0000, Seth Arnold wrote:
> On Mon, Jul 10, 2023 at 10:55:06AM +0200, Adrien Nader wrote:
> > There is a little-know but very interesting property of LZMA: its
> > decompression speed does not depend on the uncompressed size but only on
> > the compressed size. What this means is that if you compress a 100MB
> > down to 20MB, it will take roughly twice as long to decompress than if
> > you compress it down to 10MB. In other words, higher compression means
> > faster decompression.
> 
> This makes a certain amount of sense -- so much of a computer's
> operational time is spent waiting for data to arrive from memory into
> the processor, refilling cache lines, etc.
> 
> You nerd-sniped me into testing a bunch of algorithms on the
> firefox_115.0+build2.orig.tar from our archive.
> 
> I only ran these things once, and quite a lot of them ran while a
> second one was running, but this system (dual xeon E5-2630v3) has enough
> processors and memory that it probably didn't matter much.
> 
> Times in seconds, with lower level on the left, higher on the right:
> 
>          1   3   5   9
> compression:
> gzip    39  46  73 211
> zstd     8  12  23  54
> bzip2  228 237 249 265
> lzma   154 294 643 945
> xz     159 298 644 945
> 
> decompression:
> gzip    16  15  15  15
> zstd     3   3   3   3
> bzip2   68  73  74  75
> lzma    41  37  35  33
> xz      36  32  31  30
> 
> xz of course absolutely dominates the end file sizes:
> 
> 2989486080  original
> 
>  515273416  xz -9
>  625958113  zstd -9
>  647365812  xz -1
>  666820870  zstd -5  (seemed like a sweet spot in the timings)
> 
> Anyway it's fun to see that gzip and zstd have consistent decompression
> speeds, lzma and xz get faster as they go smaller, and bzip2 just gets
> slower the more it has to think.

One caveat to your whole experiment is that zstd -9 is roughly
comparable to gzip -9, whereas zstd -19 is the level comparable
to xz -9 (arguably you may also pick 17, 18 depending on how
long the compression takes vs xz -9 :D).

I think that's a reason you don't see speedups because zstd is already
quite fast and you are not really using high compression levels.
-- 
debian developer - deb.li/jak | jak-linux.org - free software dev
ubuntu core developer                              i speak de, en
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