[01] Eval/IO overhead in the greedy demo about evanix HOT 14 OPEN

https://nix.dev/manual/nix/2.23/command-ref/conf-file.html#conf-narinfo-cache-negative-ttl I would expect this setting would be used for caching cache status. You can check 'nix-build -vvvvv --dry-run' to debug in nix if this is the case.

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i tried running evanix & nix-eval-jobs on https://github.com/ggerganov/llama.cpp

$ time evanix --dry-run --system x86_64-linux --flake --max-build 555 --pipelined=false --solver-report .#packages

real    0m15.625s
user    0m0.001s
sys     0m0.004s

$ time nix-eval-jobs --force-recurse --flake .#packages

real    0m15.877s
user    0m7.297s
sys     0m3.474s

the time taken should not vary that much

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master without locality check (all drvs need to built)

$ time evanix --flake .#legacyPackages.x86_64-linux --dry-run --max-build 2147483647

real    5m35.859s
user    0m2.344s
sys     0m0.923s

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So when you say "without locality check (all drvs need to built)" you mean cost=(1, 1, ..., 1) without zeros?

yes

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the 6s nix-eval-jobs eval is probably because of only evaluating #packages.x86_64-linux
nix-eval-jobs --flake .#packages.x86_64-linux

you can get a similar performance from evanix with
evanix --dry-run --flake .#packages.x86_64-linux

where as --system x86_64-linux still evaluates everything in #packages and drops derivations with mismatched system

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Running on Nixpkgs:

❯ git rev-parse HEAD
504ca45f5c2342f36c33312be19921077f38679e
❯ time nix run github:sinanmohd/evanix -- --system x86_64-linux --flake .#legacyPackages.x86_64-linux --dry-run --max-build 50000 > evanix.stdout 2>evanix.stderr
real    263m52.738s
user    0m7.048s
sys     0m17.988s

Nix-eval-jobs finishes in just over 3 minutes:

❯ nix develop github:sinanmohd/evanix --command -- time nix-eval-jobs --flake .#legacyPackages.x86_64-linux >nix-eval-jobs.stdout 2>nix-eval-jobs.stderr
❯ tail nix-eval-jobs.stderr  -n2
200.85 user 88.72 system 9:02.31 elapsed 53% CPU (0avgtext+0avgdata 4434872maxresident)k
447568inputs+253408outputs (1major+12985415minor)pagefaults 0swaps

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master without locality check (all drvs need to built)

$ time evanix --flake .#legacyPackages.x86_64-linux --dry-run --max-build 2147483647
real    17m9.733s
user    14m35.086s
sys     0m1.427s

nix-eval-jobs

$ time nix-eval-jobs --flake .#legacyPackages.x86_64-linux
real    5m20.245s
user    3m11.060s
sys     1m11.604s

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without locality check (all drvs need to built)

How do you turn this mode on/off? WHen you turn this on, does any selection algorithm run at all (e.g. the way I imagine this is you'd compute the full closure, and generate an all-1s "value" vector)?

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the solver is still in use here, i used to have a patch on git stash
now you can use --cache-status=false on master

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the solver is still in use here, i used to have a patch on git stash

👍🏻 but what are the inputs to the solver?

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yes, if you mean cost vector by value. cache locality check sets cost to 0 for substituter cached derivatives.
but we entirely remove locally cached dependencies from the DAG.

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So when you say "without locality check (all drvs need to built)" you mean cost=(1, 1, ..., 1) without zeros?

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Btw, could you open an issue upstream (nix-eval-jobs) about --check-cache-status and include a reproducer, demonstrating the overhead present on the second and further runs? This might even be an issue with CppNix...

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