Parallel make: set -j8 as the default option

Question

I can set number of threads for the build process using -j argument. For example, I have 4 cores +4 virtual. When I write: make -j8 the speed increases 4 times.

Is it possible to set that value as default? (For example, in Linux Gentoo, in config file, it's possible to set this default value).

p.s. I have Arch Linux

Solution 1

Your question is not about threads, but processes (jobs) executed by make.

The simple, way to set this, when make is used from the console is adding:

alias make="/usr/bin/make -j 8"

to your .profile file.

You can also use setenv MAKEFLAGS '-j 8', but MAKEFLAGS can ignore this parameter in some scenarios, because keeping desired number of processes requires communicating with recursive make calls. Happily this method works with current versions of GNU Make.

Solution 2

setenv MAKEFLAGS '-j8'

Hope this helps!

Solution 3

Here's how I've done it:

CORES ?= $(shell sysctl -n hw.ncpu || echo 1)

all:; @$(MAKE) _all -j$(CORES)
_all: install lint test
.PHONY: all _all
…

I've basically "aliased" my default target all to a "private" _all. The command to figure out the number of cores is OSX specific, AFAIK, so you could just improve it to be more cross platform if you will. And because of the ?= assignment, we can just override it with and env variable if/when needed.

EDIT:

You can also append to your MAKEFLAGS from within the makefile itself, like so:

CPUS ?= $(shell sysctl -n hw.ncpu || echo 1)
MAKEFLAGS += --jobs=$(CPUS)
…

EDIT 2:

You may also use the following, ff you want it to be more cross-platform:

CPUS ?= $(shell (nproc --all || sysctl -n hw.ncpu) 2>/dev/null || echo 1)