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

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Date:	Wed, 9 Sep 2015 09:08:47 -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 Wed, 9 Sep 2015, Jesper Dangaard Brouer wrote:

> > 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.
>
> I agree, it would be an easy win.  Do notice this will have the most
> impact for the slAb allocator.
>
> I estimate alloc + free cost would save:
>  * slAb would save approx 60 cycles
>  * slUb would save approx  4 cycles
>
> We might consider keeping the slUb approach as it would be more
> friendly for RT with less IRQ disabling.

IRQ disabling it a mixed bag. Older cpus have higher latencies there and
also virtualized contexts may require the hypervisor tracks the interrupt
state.

For recent intel cpus this is certainly a workable approach.

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