[PATCH] malloc: Revert fastbins to old-style atomics

[Carlos O'Donell]

On 1/16/19 8:04 AM, Florian Weimer wrote:
> Commit 6923f6db1e688dedcf3a6556da76e0bf24a41872 ("malloc: Use current
> (C11-style) atomics for fastbin access") caused a substantial
> performance regression on POWER and Aarch64, and the old atomics,
> while hard to prove correct, seem to work in practice.

Why is it slow?

What do the benchmarks say?

What does profiling show to be the slow instruction?

How is the instruction sequence different from before that causes the problem?

-- 
Cheers,
Carlos.