bug#35139: Rust builds systematically time out

[mikadoZero <mikadozero@yandex.com>]

When I try to install rust I get similar behavior.  It does not finish
building.  The longest I have let it try for was around 12 hours. That
was is a on a machine with 1GB RAM and 10GB SWAP.

Ludovic Courtès writes:

> Hello,
>
> On berlin, Rust 1.24.1 builds systematically exceed the timeout:
>
> --8<---------------cut here---------------start------------->8---
> Building stage1 compiler artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
>    Compiling arena v0.0.0 (file:///tmp/guix-build-rust-1.24.1.drv-0/rustc-1.24.1-src/src/libarena)
>    Compiling rustc_driver v0.0.0 (file:///tmp/guix-build-rust-1.24.1.drv-0/rustc-1.24.1-src/src/librustc_driver)
>
> [...]
>
>    Compiling rls-data v0.14.0
>    Compiling rustc_data_structures v0.0.0 (file:///tmp/guix-build-rust-1.24.1.drv-0/rustc-1.24.1-src/src/librustc_data_structures)
>    Compiling flate2 v1.0.1
>    Compiling syntax_pos v0.0.0 (file:///tmp/guix-build-rust-1.24.1.drv-0/rustc-1.24.1-src/src/libsyntax_pos)
>    Compiling rustc_errors v0.0.0 (file:///tmp/guix-build-rust-1.24.1.drv-0/rustc-1.24.1-src/src/librustc_errors)
>    Compiling backtrace v0.3.4
> guix offload: error: timeout expired while offloading '/gnu/store/61bd22d9mg3xl260jwddisiahh3kmanj-rust-1.24.1.drv'
> --8<---------------cut here---------------end--------------->8---
>
> Strangely, the build lasts ~9000 seconds (2.5 hours) on the front-end
> node of berlin¹, and the timeout for guix-daemon on berlin is 6h (see
> guix-maintenance.git) while the max-silent-time is 1h.
>
> The build nodes may be slower than the front-end, but still, it seems
> unlikely that it would take more than 6h there.  (That could happen if
> the test suite, which lasts 2.1h, were “embarrassingly parallel”, but
> we’re running tests with ‘-j1’.)
>
> To summarize, there are two problems:
>
>   1. Rust takes too long to build.  What can we do about it?  Enable
>      parallel builds?
>
>   2. Offloaded builds seem to time out prematurely or something.
>
> Thoughts?
>
> Ludo’.
>
> ¹ See <https://ci.guix.info/log/rkrnm3rr7g6fhr17160vn1mz5rdzh9lv-rust-1.24.1>
>   for timings.