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Re: Robin Hood Hashing for the perl core

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From:
Dave Mitchell
Date:
September 10, 2021 12:29
Subject:
Re: Robin Hood Hashing for the perl core
Message ID:
YTtPrHeokTZMX1qr@iabyn.com
On Fri, Sep 10, 2021 at 12:21:06PM +0000, Nicholas Clark wrote:
> If I read that right
> 
> More branches.
> 
> In absolute numbers, more mispredicts for conditional branches, fewer for
> indirect branches. (Where *are* the indirect branches we're hitting so much?),

In perl, the biggest indirects are usually the per-op op->op_ppaddr(aTHX)
calls in runops()  and any switch() statements.

> In absolute numbers slightly more mispredicts over all, but proportionally
> fewer.
> 
> (Burn more CPU work with the intent to reduce cache misses)
> 
> I'm not sure what can be tweaked to be better.
> Or what actually matters, and what's fluff.
> What is the benchmark?

Your guess is as good as mine!

-- 
"But Sidley Park is already a picture, and a most amiable picture too.
The slopes are green and gentle. The trees are companionably grouped at
intervals that show them to advantage. The rill is a serpentine ribbon
unwound from the lake peaceably contained by meadows on which the right
amount of sheep are tastefully arranged." -- Lady Croom, "Arcadia"

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