On Wed, May 08, 2013 at 06:14:36PM +0200, Bastian Blank wrote: > On Tue, May 07, 2013 at 09:49:03PM +0200, Guillem Jover wrote: > > As mentioned some months ago [0], I'm planning to switch dpkg-deb default > > compressor from gzip to xz, as there seemed to be consensus that was > > the way to go, and given the amount of already manually switched > > packages, or packaging helpers. :/ > > What about the compression level? xz -6 is pretty heavy and not needed > for 99% of the packages. -3 or even -2 or -1 are sufficient.
As my and Hideki's repacks of the archive show, special-casing small packages is a waste of time: gains are hardly below linear for any packages big enough to take longer than fork()ing the compressor. Quoting some data from 2011, all with xz -6: ] * A repack of the whole archive (amd64+all main, ~40GB) took close to three ] hours on a 6xPhenomII 2.8GHz box (ar p|gzip/bzip2 -d|xz). ] ] Does someone have an estimate how many core-hours would an archive rebuild ] on such a machine take? Folks on IRC quoted numbers like "340", "240 on a ] very fast box", "more like 1500" -- too divergent for my liking. The ] first number, 340, would mean switching to xz exclusively would increase ] average build time by ~5%. ] ] * armel Cortex-A8 600MHz does xz consistently 12.1 times slower than one ] core of the above box (on a big compressible and a big uncompressible ] file), that's ~2.6 times slower per-MHz. ] ] Glancing at build logs of a few randomly chosen packages, I see armel ] builds taking respectively 16.9, 13.1, 18.8 and 15.1 times longer. Not ] sure what are the actual speeds of buildds, but it looks like armel would ] be affected by less than the above 5%. I'd thus suggest using the default, -6, everywhere other than perhaps openclipart (already compressed) and the likes. xz folks chose this value for a reason :) -- ᛊᚨᚾᛁᛏᚣ᛫ᛁᛊ᛫ᚠᛟᚱ᛫ᚦᛖ᛫ᚹᛖᚨᚲ -- To UNSUBSCRIBE, email to debian-devel-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/20130508211359.gb8...@angband.pl
