• 1 Post
  • 15 Comments
Joined 1 year ago
cake
Cake day: August 10th, 2023

help-circle



  • Sure, but my point was that such a C ABI is a pain. There are some crates that help:

    • Rust-C++: cxx and autocxx
    • Rust-Rust: stabby or abi_stable

    But without those and just plain bindgen it is a pain to transfer any types that can’t easily just be repr(C), and there are quite a few such types. Enums with data for example. Or anything using the built in collections (HashMap, etc) or any other complex type you don’t have direct control over yourself.

    So my point still stands. FFI with just bindgen/cbindgen is a pain, and lack of stable ABI means you need to use FFI between rust and rust (when loading dynamically).

    In fact FFI is a pain in most languages (apart from C itself where it is business as usual… oh wait that is the same as pain, never mind) since you are limited to the lowest common denominator for types except in a few specific cases.


  • Yes, rust is that much of a pain in this case, since you can only safely pass plain C compatible types across the plugin boundary.

    One reason is that rust doesn’t have stable layouts of structs and enums, the compiler is free to optimise the to avoid padding by reordering, decide which parts to use as niches for Options etc. And yes, that changes every now and then as the devs come up with new optimisations. I think it changes most recently last summer.


  • So there is a couple of options for plugins in Rust (and I haven’t tried any of them, yet):

    • Wasm, supposedly https://extism.org/ makes this less painful.
    • libloading + C ABI
    • One of the two stable ABI crates (stabby or abi_stable) + libloading
    • If you want to build them into your code base but not have to update a central list there is linkme and inventory.
    • An embedded scripting language might also be a (very different) option. Something like mlua, rhai or rune.

    I don’t know if any of these suit your needs, but at least you now have some things to investigate further.



  • I can second this, I use aconfmgr and love it. Especially useful to manage multiple computers (desktop, laptop, old computer doing other things etc).

    Though I’m currently planning to rewrite it since it doesn’t seem maintained any more, and I want a multi-distro solution (because I also want to use it on my Pis where I run Raspbians). The rewrite will be in Rust, and I’m currently deciding on what configuration language to use. I’m leaning towards rhai (because it seems easy to integrate from the rust side, and I’m not getting too angry at the language when reading the docs for it). Oh and one component for it is already written and published: https://github.com/VorpalBlade/paketkoll is a fast rust replacement for paccheck (that is used internally by aconfmgr to find files that differ).


  • I went ahead and implemented support for filtering packages (just made a new release: v0.1.3).

    I am of course still faster. Here are two examples that show a small package (where it doesn’t really matter that much) and a huge package (where it makes a massive difference). Excuse the strange paths, this is straight from the development tree.

    Lets check on pacman itself, and lets include config files too (not sure if pacman has that option even?). Config files or not doesn’t make a measurable difference though:

    $ hyperfine -i -N --warmup 1 "./target/release/paketkoll --config-files=include pacman" "pacman -Qkk pacman"
    Benchmark 1: ./target/release/paketkoll --config-files=include pacman
      Time (mean ± σ):      14.0 ms ±   0.2 ms    [User: 21.1 ms, System: 19.0 ms]
      Range (min … max):    13.4 ms …  14.5 ms    216 runs
     
      Warning: Ignoring non-zero exit code.
     
    Benchmark 2: pacman -Qkk pacman
      Time (mean ± σ):      20.2 ms ±   0.2 ms    [User: 11.2 ms, System: 8.8 ms]
      Range (min … max):    19.9 ms …  21.1 ms    147 runs
     
    Summary
      ./target/release/paketkoll --config-files=include pacman ran
        1.44 ± 0.02 times faster than pacman -Qkk pacman
    

    Lets check on davici-resolve as well. Which is massive (5.89 GB):

    $ hyperfine -i -N --warmup 1 "./target/release/paketkoll --config-files=include pacman davinci-resolve" "pacman -Qkk pacman davinci-resolve"
    Benchmark 1: ./target/release/paketkoll --config-files=include pacman davinci-resolve
      Time (mean ± σ):     770.8 ms ±   4.3 ms    [User: 2891.2 ms, System: 641.5 ms]
      Range (min … max):   765.8 ms … 778.7 ms    10 runs
     
      Warning: Ignoring non-zero exit code.
     
    Benchmark 2: pacman -Qkk pacman davinci-resolve
      Time (mean ± σ):     10.589 s ±  0.018 s    [User: 9.371 s, System: 1.207 s]
      Range (min … max):   10.550 s … 10.620 s    10 runs
     
      Warning: Ignoring non-zero exit code.
     
    Summary
      ./target/release/paketkoll --config-files=include pacman davinci-resolve ran
       13.74 ± 0.08 times faster than pacman -Qkk pacman davinci-resolve
    

    What about a some midsized packages (vtk 359 MB, linux 131 MB)?

    $ hyperfine -i -N --warmup 1 "./target/release/paketkoll vtk" "pacman -Qkk vtk"
    Benchmark 1: ./target/release/paketkoll vtk
      Time (mean ± σ):      46.4 ms ±   0.6 ms    [User: 204.9 ms, System: 93.4 ms]
      Range (min … max):    45.7 ms …  48.8 ms    65 runs
     
    Benchmark 2: pacman -Qkk vtk
      Time (mean ± σ):     702.7 ms ±   4.4 ms    [User: 590.0 ms, System: 109.9 ms]
      Range (min … max):   698.6 ms … 710.6 ms    10 runs
     
    Summary
      ./target/release/paketkoll vtk ran
       15.15 ± 0.23 times faster than pacman -Qkk vtk
    
    $ hyperfine -i -N --warmup 1 "./target/release/paketkoll linux" "pacman -Qkk linux"
    Benchmark 1: ./target/release/paketkoll linux
      Time (mean ± σ):      34.9 ms ±   0.3 ms    [User: 95.0 ms, System: 78.2 ms]
      Range (min … max):    34.2 ms …  36.4 ms    84 runs
     
    Benchmark 2: pacman -Qkk linux
      Time (mean ± σ):     313.9 ms ±   0.4 ms    [User: 233.6 ms, System: 79.8 ms]
      Range (min … max):   313.4 ms … 314.5 ms    10 runs
     
    Summary
      ./target/release/paketkoll linux ran
        9.00 ± 0.09 times faster than pacman -Qkk linux
    

    For small sizes where neither tool performs much work, the majority is spent on fixed overheads that both tools have (loading the binary, setting up glibc internals, parsing the command line arguments, etc). For medium sizes paketkoll pulls ahead quite rapidly. And for large sizes pacman is painfully slow.

    Just for laughs I decided to check an empty meta-package (base, 0 bytes). Here pacman actually beats paketkoll, slightly. Not a useful scenario, but for full transparency I should include it:

    $ hyperfine -i -N --warmup 1 "./target/release/paketkoll base" "pacman -Qkk base"
    Benchmark 1: ./target/release/paketkoll base
      Time (mean ± σ):      13.3 ms ±   0.2 ms    [User: 15.3 ms, System: 18.8 ms]
      Range (min … max):    12.8 ms …  14.1 ms    218 runs
     
    Benchmark 2: pacman -Qkk base
      Time (mean ± σ):       8.8 ms ±   0.2 ms    [User: 2.8 ms, System: 5.8 ms]
      Range (min … max):     8.4 ms …  10.0 ms    327 runs
     
    Summary
      pacman -Qkk base ran
        1.52 ± 0.05 times faster than ./target/release/paketkoll base
    

    I always start a threadpool regardless of if I have work to do (and changing that would slow the case I actually care about). That is the most likely cause of this slightly larger fixed overhead.



  • I have only implemented for checking all packages at the current point in time (as that is what I need later on). It could be possible to add support for checking a single package.

    Thank you for reminding me of pacman -Qkk though, I had forgotten it existed.

    I just did a test of pacman -Qk and pacman -Qkk (with no package, so checking all of them) and paketkoll is much faster. Based on the man page:

    • pacman -Qk only checks file exists. I don’t have that option, I always check file properties at least, but have the option to skip checking the file hash if the mtime and size matches (paketkoll --trust-mtime). Even though I check more in this scenario I’m still about 4x faster.
    • pacman -Qkk checks checksum as well (similar to plain paketkoll). It is unclear to me if pacman will check the checksum if the mtime and size matches.

    I can report that paketkoll handily beats pacman in both scenarios (pacman -Qk is slower than paketkoll --trust-mtime, and pacman -Qkk is much slower than plain paketkoll). Below are the output of using the hyperfine benchmarking tool:

    $ hyperfine -i -N --warmup=1 "paketkoll --trust-mtime" "paketkoll" "pacman -Qk" "pacman -Qkk"
    Benchmark 1: paketkoll --trust-mtime
      Time (mean ± σ):     246.4 ms ±   7.5 ms    [User: 1223.3 ms, System: 1247.7 ms]
      Range (min … max):   238.2 ms … 261.7 ms    11 runs
     
      Warning: Ignoring non-zero exit code.
     
    Benchmark 2: paketkoll
      Time (mean ± σ):      5.312 s ±  0.387 s    [User: 17.321 s, System: 13.461 s]
      Range (min … max):    4.907 s …  6.058 s    10 runs
     
      Warning: Ignoring non-zero exit code.
     
    Benchmark 3: pacman -Qk
      Time (mean ± σ):     976.7 ms ±   5.0 ms    [User: 101.9 ms, System: 873.5 ms]
      Range (min … max):   970.3 ms … 984.6 ms    10 runs
     
    Benchmark 4: pacman -Qkk
      Time (mean ± σ):     86.467 s ±  0.160 s    [User: 53.327 s, System: 16.404 s]
      Range (min … max):   86.315 s … 86.819 s    10 runs
     
      Warning: Ignoring non-zero exit code.
    

    It appears that pacman -Qkk is much slower than paccheck --file-properties --sha256sum even. I don’t know how that is possible!

    The above benchmarks were executed on an AMD Ryzen 5600X with 32 GB RAM and an Gen3 NVME SSD. pacman -Syu executed as of yesterday most recently. Disk cache was hot in between runs for all the tools, that would make the first run a bit slower for all the tools (but not to a large extent on a SSD, I can imagine it would dominate on a mechanical HDD though)

    In conclusion:

    • When checking just file properties paketkoll is 3.96 times faster than pacman checking just if the files exist
    • When checking checksums paketkoll is 16.3 times faster than pacman checking file properties. This is impressive on a 6 core/12 thread CPU. pacman must be doing something exceedingly stupid here (might be worth looking into, perhaps it is checking both sha256sum and md5sum, which is totally unneeded). Compared to paccheck I see a 7x speedup in that scenario which is more in line with what I would expect.





  • Be sure to treat state and configuration separately. It doesn’t matter on Windows as far as I know (they go in the same location), but on Linux those are supposed to go in different places.

    Many programs get this wrong, and it is quite annoying as I track my config files in git. I don’t want a diff just because the list of recently opened files changed! Or even worse: the program stores the last window size and position in the config file… (looking at you KDE!)

    Here are some libraries I found to help with this in a cross platform way:

    I haven’t tried either, haven’t written such a program yet.

    As for how to store data, there are indeed many options, depending on your needs:

    • Plain text based formats (toml, yaml, JSON, ini, …) can be good for configs and basic state. As a bonus it let’s the user easily manage the file in version control if they are so inclined.
    • Databases (SQLite mostly)
    • Custom formats (binary files in a directory structure is often used for browser caches for example) .

    Without knowing more it is hard to give specific advise.