[Twirrim]

I tried a few times with zstd at various levels of compression with the linux kernel sources. While I've been impressed with zstd, and have some projects lined up to use it, it seems in the case of the linux kernel sources, it's not a great fit. xz handily beats it, and not by a small margin either. I had to really ratchet up the compression levels (20+) before I could get close to 100Mb.

[Iburinoc]

In general, xz beats zstd in compression ratio, as xz is very committed to providing the strongest compression, at the expense of speed, while zstd provides a range of compression ratio vs speed tradeoffs [0]. At the lower levels, zstd isn't approaching xz's compression level, but it's doing it much much faster. Additionally, zstd generally massively outperforms xz in decompression speed

  $ time xz linux-4.14-rc6.tar

  real    4m26.009s
  user    4m24.828s
  sys     0m0.724s

  $ wc -c linux-4.14-rc6.tar.xz
  103705148 linux-4.14-rc6.tar.xz

  $ time zstd --ultra -20 linux-4.14-rc6.tar
  linux-4.14-rc6.tar   : 12.81%   (824350720 => 105564246 bytes, linux-4.14-rc6.tar.zst)

  real    4m34.129s
  user    4m33.484s
  sys     0m0.432s

  $ time cat linux-4.14-rc6.tar.xz | xz -d > out1                                                                                                                                           

  real    0m9.677s
  user    0m6.608s
  sys     0m0.704s

  $ time cat linux-4.14-rc6.tar.zst | zstd -d > out2

  real    0m1.702s
  user    0m1.220s
  sys     0m0.520s

[0]: https://github.com/facebook/zstd/blob/dev/doc/images/DCspeed...