[llvm-dev] Building with LLVM_PARALLEL_XXX_JOBS

[Mehdi Amini via llvm-dev]

> On Feb 24, 2016, at 9:55 PM, Sedat Dilek via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi,
> 
> I switched from "configure and make" to "cmake" build-system and
> wanted to speedup my build.
> 
> In my build-script I use...
> 
> CMAKE_JOBS="1"
> ##CMAKE_JOBS=$(($(getconf _NPROCESSORS_ONLN)+1))
> JOBS_CMAKE_OPTS="-DLLVM_PARALLEL_COMPILE_JOBS=$CMAKE_JOBS
> -DLLVM_PARALLEL_LINK_JOBS=$CMAKE_JOBS"
> 
> [1] says in "LLVM-specific variables" section...
> 
> *** LLVM_PARALLEL_COMPILE_JOBS:STRING
> 
> Define the maximum number of concurrent compilation jobs.
> 
> *** LLVM_PARALLEL_LINK_JOBS:STRING
> 
> Define the maximum number of concurrent link jobs.
> 
> ...whereas my configure-log says...
> 
> $ grep -i job -A1 logs/configure-log_llvm-toolchain-3.8.0rc3.txt
>  Job pooling is only available with Ninja generators and CMake 3.0 and
>  later.
> --
>  Job pooling is only available with Ninja generators and CMake 3.0 and
>  later.
> 
> My cmake-version is...
> 
> $ cmake --version
> cmake version 2.8.12.2
> 
> So, I need Ninja *and* CMake >= v3.0 (or is the right CMake version
> sufficient) to use LLVM_PARALLEL_XXX_JOBS?

Yes. When you run ninja without any argument you have parallelism by default. This options can control the default number of jobs for ninja. 
Also, especially when doing LTO, you may want to limit the number of link jobs independently from the number of compile job, which is again a facility that ninja has.

> If this is a fact, can you please adjust the information in [1]?
> 
> Do I have other options to speedup my build?

Yes: start to use ninja ;)
If for any reason (?) you are really stuck with "make", then run "make -j ~ncpus" (with ~ncpus "approximately the number of cores in your machine). It will build in parallel.

-- 
Mehdi



> ( For testing RCs I tend to use slow build - one single (c)make job. )
> 
> My build-script and configure-log are attached.
> 
> Thanks.
> 
> Regards,
> - Sedat -
> 
> 
> [1] http://llvm.org/docs/CMake.html
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