[llvm-dev] LLD benchmark results for all commits

[Rafael Espíndola via llvm-dev]

Thanks a lot for doing this.

Yes, a perf bot that would just link clang over and over in a quiet
environment would be awesome.

Cheers,
Rafael


On 15 January 2016 at 17:42, Rui Ueyama via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Speed is one of the most important goals for the new ELF linker. I ran a
> benchmark for every commit to LLD/ELF that was made after the last October,
> and I'd like to share the result. The motivation is to see if the linker is
> getting slower as we add more features, and if so, which commits are heavy
> ones in terms of performance. I measured time to link the same Clang
> executable.
>
> Here is the result. This table contains a commit message, a SVN revision
> number, time to link, size of the resulting Clang binary in each row.
>
> https://docs.google.com/spreadsheets/d/1QlQZ51VQUna6gX0qXj19v_ZEII5vGaHrUhBKq-Z_9uc/edit?usp=sharing
>
> As you can see, the linker is faster than the original. A few key findings
> are listed below:
>
>  - The linker tend to be gradually getting slower over time in general.
>  - There are a few commits that increased link time by a few percent or
> more.
>  - However, we also committed a few performance improvement changes to
> offset them.
>
> The commit that increased link time most (+15%) is r251212: Add support for
> merging string from SHF_STRINGS sections. This does not come as a surprise
> since string merging is a computationally heavy operation.
>
> The commit that decreased link time most (-29%) is r250315: ELF2: Merge
> .{text,rodata,data,bss}.* sections. This is because the commit significantly
> decreased number of sections in the output.
>
> The following commits are also noteworthy.
>
>  - r257017: ELF: Improve performance of string table construction (-14.0%)
>  - r251332: Optimize StringTableBuilder (-7.8%)
>
> Ideally, we should have a perf bot to run a benchmark for every commit, so
> that we do not accidentally commit changes that hurt performance.
>
> Overall, I'm satisfied with the result. It found no commit that increases
> link time for no justifiable reason.
>
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