[lld] r287042 - Use one task per iteration in parallel_for_loop.

[Rui Ueyama via llvm-commits]

Can you try to run your benchmark again without --build-id? For me, this
patch slows down the linker by about 30% with --threads and without
--build-id.

On Tue, Nov 15, 2016 at 2:13 PM, Rafael Espindola via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: rafael
> Date: Tue Nov 15 16:13:16 2016
> New Revision: 287042
>
> URL: http://llvm.org/viewvc/llvm-project?rev=287042&view=rev
> Log:
> Use one task per iteration in parallel_for_loop.
>
> This seems far more natural. A user can create larger chunks if the
> overhead is too large.
>
> With this linking xul with "--threads --build-id=sha1 goes from
> 13.938177535 to 11.035953538 seconds on linux.
>
> Modified:
>     lld/trunk/include/lld/Core/Parallel.h
>
> Modified: lld/trunk/include/lld/Core/Parallel.h
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/include/lld/
> Core/Parallel.h?rev=287042&r1=287041&r2=287042&view=diff
> ============================================================
> ==================
> --- lld/trunk/include/lld/Core/Parallel.h (original)
> +++ lld/trunk/include/lld/Core/Parallel.h Tue Nov 15 16:13:16 2016
> @@ -284,12 +284,8 @@ void parallel_for_each(Iterator begin, I
>  template <class Iterator, class Func>
>  void parallel_for_each(Iterator begin, Iterator end, Func func) {
>    TaskGroup tg;
> -  ptrdiff_t taskSize = 1024;
> -  while (taskSize <= std::distance(begin, end)) {
> -    tg.spawn([=, &func] { std::for_each(begin, begin + taskSize, func);
> });
> -    begin += taskSize;
> -  }
> -  std::for_each(begin, end, func);
> +  for (; begin != end; ++begin)
> +    tg.spawn([=, &func] { func(*begin); });
>  }
>  #endif
>  } // end namespace lld
>
>
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