netdev - Re: atomic operations bottleneck in the IPv6 stack

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Date:	Wed, 10 Dec 2014 18:58:30 +0100
From:	Hannes Frederic Sowa <hannes@...hat.com>
To:	"cristian.bercaru@...escale.com" <cristian.bercaru@...escale.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"R89243@...escale.com" <R89243@...escale.com>,
	Madalin-Cristian Bucur <madalin.bucur@...escale.com>,
	"Razvan.Ungureanu@...escale.com" <Razvan.Ungureanu@...escale.com>
Subject: Re: atomic operations bottleneck in the IPv6 stack

On Mi, 2014-12-10 at 18:16 +0100, Hannes Frederic Sowa wrote:
> On Mi, 2014-12-10 at 16:56 +0000, cristian.bercaru@...escale.com wrote:
> > 
> > It seems to me that the atomic operations on the IPv6 forwarding path
> > are a bottleneck and they are not scalable with the number of cores.
> > Am I right? What improvements can be brought to the IPv6 kernel code
> > to make it less dependent of atomic operations/variables?
> 
> For a starter, something like the following commit:
> 
> commit d26b3a7c4b3b26319f18bb645de93eba8f4bdcd5
> Author: Eric Dumazet <edumazet@...gle.com>
> Date:   Tue Jul 31 05:45:30 2012 +0000
> 
>     ipv4: percpu nh_rth_output cache

Actually, we should be able to remove the atomics in input and
forwarding path by just relying on RCU. I'll have a look.

Bye,
Hannes


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