[PATCH] D36351: [lld][ELF] Add profile guided section layout

[Michael Spencer via llvm-commits]

On Thu, Feb 1, 2018 at 10:06 AM, Rafael Avila de Espindola <
rafael.espindola at gmail.com> wrote:

> Rafael Avila de Espindola <rafael.espindola at gmail.com> writes:
>
> I tested the patch by linking chromium.
>
> With the last version of the patch I can measure a small improvement in
> L1-icache-load-misses. Somehow iTLB-load-misses seems to get worse:
>
>  Performance counter stats for './default-ld.lld @response.txt -o t
> --no-threads' (20 runs):
>
>            279,008      iTLB-load-misses
>             ( +-  0.36% )
>         17,916,925      L1-icache-load-misses
>            ( +-  0.19% )
>
>        1.165371143 seconds time elapsed
>       ( +-  0.12% )
>
>
>  Performance counter stats for './sorted-ld.lld @response.txt -o t
> --no-threads' (20 runs):
>
>            289,396      iTLB-load-misses
>             ( +-  0.77% )
>         16,922,395      L1-icache-load-misses
>            ( +-  0.18% )
>
>        1.166535009 seconds time elapsed
>       ( +-  0.12% )
>
> Do you have a suggestion of an open source program that might benefit
> more from this optimization?
>
> Cheers,
> Rafael
>

I don't expect this patch to have a large impact on lld as its working set
is rather small. Peter Collingbourne previously tested this patch on Chrome
and got rather good results. He's already CCed, so I pinged him on IRC to
see if he can chime in.

- Michael Spencer
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