On 3/25/19 1:38 AM, Evangelos Foutras via arch-dev-public wrote: > On Mon, 25 Mar 2019 at 01:22, Jan Alexander Steffens via > arch-dev-public <arch-dev-public@archlinux.org> wrote: >> >> When we implement this, I would say we go with "zstd -c -T0 -" in >> pacman's makepkg.conf and "zstd -C -T0 -18 -" in the configs shipped >> with devtools. >> >> I think users that build their own local packages are more likely to >> benefit from fast compression. Anyone building with makechrootpkg for >> distribution gets the high compression level. > > That's actually really smart! We can also leave out "-T0" since the > default compression level is very fast anyway. Plus, it's already > implemented in this way in pacman git so we don't have to touch > anything there. (But, if it were to be multithreaded there as well, I > would replace zstd with zstdmt; same for devtools.)
That's why the subject line is prefixed with '(devtools)' :) What's unclear to me is the difference between zstd -T0 and zstdmt, however. > > As far as compression level goes, I believe we should select the > highest one that doesn't have increased memory requirements during > decompression. So that would be -19. Robin makes a good case about > -18; looking at upstream's "Compression Speed vs Ratio" graph [1] I > would say -18 is preferable to -19 if we are concerned about > compression speed and memory usage (my totally unscientific > measurements show a 25% memory increase and 20% speed decrease going > from -18 to -19 when using -T4). That said, I might still opt for -19 > due to the slightly higher compression ratio; memory usage isn't too > big of an issue and the slower speed is mitigated by multithreading > (i.e.: it will still be much faster than xz). > I do think that at -19+, memory usage becomes a bigger issue. The difference between -18 and -19 on cuda is almost a gigabyte! While not really a problem for our beefy build boxes, some 4- or even 8-GB developer machines could really suffer from such an incline in memory usage. Thus i stand by -18 being the more sensible choice. Rob
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