netdev - Re: [RFC PATCH] slub: RFC: Improving SLUB performance with 38% on NO-PREEMPT

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Date:	Thu, 04 Jun 2015 19:37:57 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Alexander Duyck <alexander.duyck@...il.com>,
	linux-mm@...ck.org, netdev@...r.kernel.org
Subject: Re: [RFC PATCH] slub: RFC: Improving SLUB performance with 38% on
 NO-PREEMPT

On Thu, 2015-06-04 at 12:31 +0200, Jesper Dangaard Brouer wrote:
> This patch improves performance of SLUB allocator fastpath with 38% by
> avoiding the call to this_cpu_cmpxchg_double() for NO-PREEMPT kernels.
> 
> Reviewers please point out why this change is wrong, as such a large
> improvement should not be possible ;-)

I am not sure if anyone already answered, but the cmpxchg_double()
is needed to avoid the ABA problem.

This is the whole point using tid _and_ freelist

Preemption is not the only thing that could happen here, think of
interrupts.



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