[Nix-dev] Re: make -jx within builds?

[Jeff Johnson]

On May 29, 2010, at 5:39 PM, Marc Weber wrote:

> Does it even make sense to ask nix to add -j $NUM_CORES -l $NUM_CORES to
> makeFlags if NUM_CORES is > 1 ?
> 
> Then we don't even have to change build scripts. So we don't have to
> wait for an stdenv-updates merge to use this new feature..
> 

Here's a gentle hint on how to implement NUM_CORES based on hysterical
experiences with RPM ...

While build "recipes" are just thinly disguised scripts, and
make options like -j $NUM_CORES -l $NUM_CORES (and whatever else you wish)
can be added explicitly to the commands in the recipe, one
should strive to make the gory details of the build "system"
as opaque as possible to the build "recipe".

There are too many possible policies/heuristics for choosing
options passed to make, and there are also too many ways
to gain info about the build "system" (like #cpus and loadavg and ...)
to expose the details portably.

Instead, I'd choose an "opt-in" (or conversely "opt-out") approach
as a default rule for invoking make(1) with opaque options that
are set from the build "system", not the build "recipe", and
then add a means to to deal with "recipes" that do not conform
to the general rule.

I hope that is what you are attempting to implement.

hth

73 de Jeff