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Re: [PATCH] alternative hirate for builtin_expert
- From: Rong Xu <xur at google dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Cc: Jan Hubicka <hubicka at ucw dot cz>, David Li <davidxl at google dot com>
- Date: Tue, 1 Oct 2013 10:08:58 -0700
- Subject: Re: [PATCH] alternative hirate for builtin_expert
- Authentication-results: sourceware.org; auth=none
- References: <CAF1bQ=TH5+Qfd1MsAUDBJj+F-zizymTTGh7HxyuXUbaPqd-mng at mail dot gmail dot com>
On Fri, Sep 27, 2013 at 3:53 PM, Rong Xu <email@example.com> wrote:
> 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
> 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