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Date: Wed, 17 Feb 2016 09:13:25 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
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To: Waiman Long <Waiman.Long@hpe.com>
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        Douglas Hatch <doug.hatch@hp.com>
Subject: Re: [RFC PATCH 1/2] lib/percpu-list: Per-cpu list with associated
 per-cpu locks
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On Tue, 16 Feb 2016, Waiman Long wrote:

> List entry insertion is strictly per cpu. List deletion, however, can
> happen in a cpu other than the one that did the insertion. So we still
> need lock to protect the list. Because of that, there may still be
> a small amount of contention when deletion is being done.

Is there a way to avoid locking completely? You could use cmpxchg_double
to swap both list head and tail in an atomic fashion with some work. There is
even a this_cpu_cmpxchg_double available.