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Re: [PATCH] alternative hirate for builtin_expert


ping.

On Fri, Sep 27, 2013 at 3:53 PM, Rong Xu <xur@google.com> wrote:
> Hi,
>
>
>
>   Current default probability for builtin_expect is 0.9996.
> This makes the freq of unlikely bb very low (4), which
> suppresses the inlining of any calls within those bb.
>
> We used FDO data to measure the branch probably for
> the branch annotated with builtin_expert.
> For google internal benchmarks, the weight average
> (the profile count value as the weight) is 0.9081.
>
> Linux kernel is another program that is heavily annotated
> with builtin-expert. We measured its weight average as 0.8717,
> using google search as the workload.
>
> This patch sets the alternate hirate probability for builtin_expert
> to 90%. With the alternate hirate, we measured performance
> improvement for google benchmarks and Linux kernel.
>
> An earlier discussion is
> https://mail.google.com/mail/u/0/?pli=1#label/gcc-paches/1415c5910054630b
>
> This new patch is for the trunk and addresses Honza's comments.
>
> Honza: this new probability is off by default. When we backport to google
> branch we will make it the default. Let me know if you want to do the same
> here.
>
> Thanks,
>
> -Rong


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