netdev - Re: [RFC PATCH 0/3] Network stack, first user of SLAB/kmem

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Date:	Tue, 8 Sep 2015 12:32:40 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
cc:	Alexander Duyck <alexander.duyck@...il.com>,
	netdev@...r.kernel.org, akpm@...ux-foundation.org,
	linux-mm@...ck.org, aravinda@...ux.vnet.ibm.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	iamjoonsoo.kim@....com
Subject: Re: [RFC PATCH 0/3] Network stack, first user of SLAB/kmem_cache
 bulk free API.

On Sat, 5 Sep 2015, Jesper Dangaard Brouer wrote:

> The double_cmpxchg without lock prefix still cost 9 cycles, which is
> very fast but still a cost (add approx 19 cycles for a lock prefix).
>
> It is slower than local_irq_disable + local_irq_enable that only cost
> 7 cycles, which the bulking call uses.  (That is the reason bulk calls
> with 1 object can almost compete with fastpath).

Hmmm... Guess we need to come up with distinct version of kmalloc() for
irq and non irq contexts to take advantage of that . Most at non irq
context anyways.

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