Multi-Threaded make

[Gabriel VLASIU]

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On Thu, 29 Nov 2012, David G. Miller wrote:

> Setting -j to be equal to the number of cores/CPUs is just playing it 
> safe.
Yes, this is the default behavior of rpmbuild:

%_smp_mflags is defined in /usr/lib/rpm/redhat/macros:

%_smp_mflags %([ -z "$RPM_BUILD_NCPUS" ] \\\
	&& RPM_BUILD_NCPUS="`/usr/bin/getconf _NPROCESSORS_ONLN`"; \\\
        if [ "$RPM_BUILD_NCPUS" -gt 16 ]; then echo "-j16"; \\\
        elif [ "$RPM_BUILD_NCPUS" -gt 1 ]; then echo "-j$RPM_BUILD_NCPUS"; fi)

> This is especially true when building a rpm which involves not just 
> compiles and link but also packaging, dependency resolution and 
> documentation tasks which are even more disk I/O intensive than 
> compiles.  Chances are that several of these operations that not 
> dependent on successfully compiling the code are fired off in parallel 
> rather than doing them sequentially and that old workhorse make gets the 
> task of managing each of these tasks.
I disagree with you here. You build a rpm in stages: "%prep", "%build", 
"%install", "list check for %files" and packaging (dependency 
resolution/debug-info/etc). Each stage is dependent on the previous one.
All the stages are run sequentially.
make (%build stage) and make install (%install stage) may run things in 
parallel. But this is something else (as I understand the process).

> Thus, you end up with multiple copies of make running at the same time 
> even on a single core/CPU system to perform these tasks.
Exactly. This is what I was trying to explain to JD( jd1008@).
make != cc1.
make can spawn more make processes which eventually can run cc1. 

Sorry but English is not my first language.

> My best results were with -j 12.
Wow! :-)


Gabriel

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// Gabriel VLASIU
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