[PATCH] benchtests: Build benchmarks in parallel

[Sam James]

Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:

> The unconditional '.NOTPARALLEL' in benchtests/Makefile forced the whole
> subdirectory to build serially, even though its only purpose is to keep
> the benchmark *runs* from perturbing each other's timing.
>
> Replace it with ordering that serializes only the benchmark runs, and
> only when more than one benchmark group will actually run.  The combined
> 'bench' goal builds every benchmark program in parallel (through
> bench-build) and then runs the bench-set, bench-func and bench-malloc
> groups strictly one after another.
> ---
>  benchtests/Makefile | 27 ++++++++++++++++++++++++---
>  1 file changed, 24 insertions(+), 3 deletions(-)
>
> diff --git a/benchtests/Makefile b/benchtests/Makefile
> index 53f78232ffe..f407e492cb7 100644
> --- a/benchtests/Makefile
> +++ b/benchtests/Makefile
> @@ -409,9 +409,9 @@ $(addprefix $(objpfx)bench-,calloc-thread): $(libm-benchtests)
>  # Rules to build and execute the benchmarks.  Do not put any benchmark
>  # parameters beyond this point.
>  
> -# We don't want the benchmark programs to run in parallel since that could
> -# affect their performance.
> -.NOTPARALLEL:
> +# Benchmark programs must not run concurrently, however building them is
> +# safe in parallel.  So '.NOTPARALLEL:' is used only when benchmarks run
> +# or when more than one group is going to run.
>  
>  bench-extra-objs = json-lib.o
>  
> @@ -627,3 +627,24 @@ $(objpfx)bench-%.c: %-inputs $(bench-deps)
>  	fi; \
>  	$(PYTHON) scripts/bench.py $(patsubst %-inputs,%,$<); } > $@-tmp
>  	mv -f $@-tmp $@
> +
> +# Serialize the benchmark runs so their timing is not perturbed by a
> +# concurrent workload, while still building every benchmark program in parallel.
> +# Ordering is only needed when more than one benchmark group run: the combined
> +# 'bench' goal runs all three groups, and the bench* goals can also be combined
> +# on a single command line.  A lone group needs no ordering -- make builds its
> +# programs in parallel and then runs its single recipe, which cannot overlap a
> +# compile.
> +ifneq (,$(filter bench,$(MAKECMDGOALS)))
> +bench-run-active := bench-set bench-func bench-malloc
> +else
> +bench-run-active := $(filter bench-set bench-func bench-malloc,$(MAKECMDGOALS))
> +endif
> +
> +ifneq (,$(word 2,$(bench-run-active)))
> +# Hold every active run until all benchmark programs have been built.
> +$(bench-run-active): | bench-build
> +# And then run the active groups strictly one at a time.
> +bench-func: | $(filter bench-set,$(bench-run-active))
> +bench-malloc: | $(filter bench-set bench-func,$(bench-run-active))
> +endif

Reviewed-by: Sam James <sam@gentoo.org>
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