Downloading of repodata with linux-musl pixi builds can be very slow

[Hofer-Julian]

Checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pixi, using pixi --version.

Reproducible example

git clone ssh://[email protected]/holoviz/holoviews.git
cd holoviews
rm -f pixi.lock; pixi install

Issue description

On my machine, installation nearly comes to a halt.
On @ruben-arts's machine, the issue isn't easily reproducible.

Expected behavior

Installing works fine

[Hofer-Julian]

@ruben-arts and I, could pin it down to musl on linux.
It is reproducible for older pixi releases as well.
On Linux with glibc or other platforms the issue doesn't appear.
Unfortunately, @baszalmstra PR to use faster allocators with musl doesn't help here: #2874

We should profile to figure out which musl function is to blame for this slowdown compared to glibc.

[ruben-arts]

After building it correctly, it did indeed improve and resolve this issue (I would say) completely.

❯ hyperfine -p "rm pixi.lock -f" "pixi-perf-musl list --no-install" "pixi list --no-install" -r 3 -w 1
# THIS PR WITH `--feature performance`
Benchmark 1: pixi-perf-musl list --no-install
  Time (mean ± σ):     10.475 s ±  0.296 s    [User: 121.102 s, System: 10.084 s]
  Range (min … max):   10.260 s … 10.813 s    3 runs
# THIS PR WITHOUT THE `--feature performance`
Benchmark 2: pixi list --no-install
  Time (mean ± σ):     132.517 s ±  3.027 s    [User: 517.171 s, System: 1443.620 s]
  Range (min … max):   129.974 s … 135.865 s    3 runs
 
Summary
  pixi-perf-musl list --no-install ran
   12.65 ± 0.46 times faster than pixi list --no-install