[lld] r232460 - [ELF] Use parallel_for_each for writing.

[Sean Silva]

On Mon, Mar 16, 2015 at 8:29 PM, Shankar Easwaran <shankare at codeaurora.org>
wrote:

> Author: shankare
> Date: Mon Mar 16 22:29:32 2015
> New Revision: 232460
>
> URL: http://llvm.org/viewvc/llvm-project?rev=232460&view=rev
> Log:
> [ELF] Use parallel_for_each for writing.
>
> This changes improves performance of lld, when self-hosting lld, when
> compared
> with the bfd linker. BFD linker on average takes 8 seconds in elapsed time.
> lld takes 3 seconds elapased time average. Without this change, lld takes
> ~5
> seconds average. The runtime comparisons were done on a release build and
> measured by running linking thrice.
>
> lld self-host without the change
> ----------------------------------
> real    0m3.196s
> user    0m4.580s
> sys     0m0.832s
>
> lld self-host with lld
> -----------------------
> user    0m3.024s
> user    0m3.252s
> sys     0m0.796s
>
> time taken to build lld with bfd
> --------------------------------
> real    0m8.419s
> user    0m7.748s
> sys     0m0.632s
>
> Modified:
>     lld/trunk/lib/ReaderWriter/ELF/OutputELFWriter.h
>     lld/trunk/lib/ReaderWriter/ELF/SectionChunks.h
>
> Modified: lld/trunk/lib/ReaderWriter/ELF/OutputELFWriter.h
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/ELF/OutputELFWriter.h?rev=232460&r1=232459&r2=232460&view=diff
>
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/ELF/OutputELFWriter.h (original)
> +++ lld/trunk/lib/ReaderWriter/ELF/OutputELFWriter.h Mon Mar 16 22:29:32
> 2015
> @@ -586,8 +586,10 @@ std::error_code OutputELFWriter<ELFT>::w
>    _elfHeader->write(this, _layout, *buffer);
>    _programHeader->write(this, _layout, *buffer);
>
> -  for (auto section : _layout.sections())
> -    section->write(this, _layout, *buffer);
> +  auto sections = _layout.sections();
> +  parallel_for_each(
> +      sections.begin(), sections.end(),
> +      [&](Chunk<ELFT> *section) { section->write(this, _layout, *buffer);
> });
>    writeTask.end();
>
>    ScopedTask commitTask(getDefaultDomain(), "ELF Writer commit to disk");
>
> Modified: lld/trunk/lib/ReaderWriter/ELF/SectionChunks.h
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/ELF/SectionChunks.h?rev=232460&r1=232459&r2=232460&view=diff
>
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/ELF/SectionChunks.h (original)
> +++ lld/trunk/lib/ReaderWriter/ELF/SectionChunks.h Mon Mar 16 22:29:32 2015
> @@ -234,17 +234,17 @@ public:
>    /// routine gets called after the linker fixes up the virtual address
>    /// of the section
>    virtual void assignVirtualAddress(uint64_t addr) override {
> -    for (auto &ai : _atoms) {
> +    parallel_for_each(_atoms.begin(), _atoms.end(), [&](AtomLayout *ai) {
>        ai->_virtualAddr = addr + ai->_fileOffset;
> -    }
> +    });
>    }
>
>    /// \brief Set the file offset of each Atom in the section. This routine
>    /// gets called after the linker fixes up the section offset
>    void assignFileOffsets(uint64_t offset) override {
> -    for (auto &ai : _atoms) {
> +    parallel_for_each(_atoms.begin(), _atoms.end(), [&](AtomLayout *ai) {
>        ai->_fileOffset = offset + ai->_fileOffset;
> -    }
> +    });
>    }
>
>
It looks like we only ever do `_atoms.push_back(new (_alloc)
lld::AtomLayout(...));` can we just store the AtomLayout's by value in the
vector? It seems like that would be simpler and also make these loops a lot
more cache friendly.

-- Sean Silva


>    /// \brief Find the Atom address given a name, this is needed to
> properly
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20150316/293665a2/attachment.html>