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Make -j flag less exceptional (#22360)

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* Make -j flag less exceptional

The -j flag in spack behaves differently from make, ctest, ninja, etc,
because it caps the number of jobs to an arbitrary number 16.
Spack will behave like other tools if `spack install` uses a reasonable
default, and `spack install -j <num>` *overrides* that default.

This will be particularly useful for Spack usage outside of a traditional
HPC context and for HPC centers that encourage users to compile on
login nodes with many cores instead of on compute nodes, which has
become increasingly common as individual nodes have more cores.

This maintains the existing default value of min(num_cpus, 16). However, 
as it is right now, Spack does a poor job at determining the number of 
cpus on linux, since it doesn't take cgroups into account. This is
particularly problematic when using distributed builds with slurm. This PR
also introduces `spack.util.cpus.cpus_available()` to consolidate
knowledge on determining the number of available cores, and improves
core detection for linux. This should also improve core detection for Docker/
Kubernetes, which also use cgroups.
This commit is contained in:
Harmen Stoppels
2021-03-30 21:03:50 +02:00
committed by GitHub
parent d3a9824ea2
commit 1db6cd5d16
8 changed files with 97 additions and 44 deletions
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12
etc/spack/defaults/config.yaml
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@@ -142,11 +142,13 @@ config:
locks: true
# The maximum number of jobs to use when running `make` in parallel,
# always limited by the number of cores available. For instance:
# - If set to 16 on a 4 cores machine `spack install` will run `make -j4`
# - If set to 16 on a 18 cores machine `spack install` will run `make -j16`
# If not set, Spack will use all available cores up to 16.
# The maximum number of jobs to use for the build system (e.g. `make`), when
# the -j flag is not given on the command line. Defaults to 16 when not set.
# Note that the maximum number of jobs is limited by the number of cores
# available, taking thread affinity into account when supported. For instance:
# - With `build_jobs: 16` and 4 cores available `spack install` will run `make -j4`
# - With `build_jobs: 16` and 32 cores available `spack install` will run `make -j16`
# - With `build_jobs: 2` and 4 cores available `spack install -j6` will run `make -j6`
# build_jobs: 16