[Nix-dev] `fast-eval' branch merged

[Nicolas Pierron]

Hi,

Great News :)

On Wed, May 12, 2010 at 16:01, Eelco Dolstra <e.dolstra at tudelft.nl> wrote:
> Hi,
>
> I've merged the Nix `fast-eval' branch into the trunk.  This replaces the
> current Nix expression evaluator by a new, faster implementation.  It no longer
> uses the term-rewriting based approach (described in [1]) but a more
> conventional functional language implementation based on thunk updating.  As a
> result, Nix no longer depends on the ATerm library.
>
> Here are some benchmark results to show the performance improvement.  The
> benchmarks are:
>
> - `nix-env -f /etc/nixos/nixpkgs -qa \*' on Nixpkgs r21747.
> - `nix-env -f /etc/nixos/nixpkgs -qa \* --drv-path'.
> - `nix-instantiate /etc/nixos/nixos -A system --readonly-mode' (also on r21747
> of NixOS).  This is what every `nixos-rebuild' operation does.
> - `nix-instantiate /etc/nixos/nixos/tests/ -A proxy.test --readonly-mode' (which
> evaluates 4 NixOS system configurations).
>
> These were done on a 32-bit Linux machine (Intel Core 2 Duo T7700 @ 2.40GHz, 2
> GiB RAM) and on a 64-bit Linux machine (Intel Core i5 750 @ 2.67GHz, 6 GiB RAM).
>  Here are the timings in seconds:
>
>                                         | Old   | New  | Speedup
> -----------------------------------------+-------+------+--------
> `nix-env -qa' (32-bit)                   |  2.96 | 0.60 | 4.9x
> `nix-env -qa' (64-bit)                   |  1.86 | 0.32 | 5.8x
> `nix-env -qa --drv-path' (32-bit)        | 12.48 | 3.96 | 3.2x
> `nix-env -qa --drv-path' (64-bit)        |  7.65 | 2.04 | 3.8x
> `nix-instantiate -A system' (32-bit)     |  6.79 | 1.32 | 5.1x
> `nix-instantiate -A system' (64-bit)     |  4.63 | 0.71 | 6.5x
> `nix-instantiate -A proxy.test' (32-bit) | 23.86 | 3.55 | 6.7x
> `nix-instantiate -A proxy.test' (64-bit) | 15.76 | 1.95 | 8.1x
>
> Another goal of the `fast-eval' branch was to reduce memory consumption by the
> evaluator.  The old evaluator basically never released memory due to its normal
> form cache.  With the new evaluator, we can in principle reclaim garbage memory.
>  However, it doesn't actually have a garbage collector yet.  I intend to use the
> Boehm GC for that.  Nevertheless, the new evaluator already uses less memory
> than the old one.  For instance, `nix-instantiate -A system' on 64-bit Linux
> uses 358.6 MiB with the old evaluator, but only 213.7 MiB with the new evaluator
> (according to Valgrind's `massif' tool).
>
> [1] http://www.st.ewi.tudelft.nl/~dolstra/pubs/laziness-ldta2008-final.pdf




-- 
Nicolas Pierron
http://www.linkedin.com/in/nicolasbpierron - http://nbp.name/