netdev - Re: [net-next PATCH v3 00/12] Flow API

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Message-ID: <20150123160058.GN25797@casper.infradead.org>
Date:	Fri, 23 Jan 2015 16:00:58 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	John Fastabend <john.fastabend@...il.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	simon.horman@...ronome.com, sfeldma@...il.com,
	netdev@...r.kernel.org, davem@...emloft.net, gerlitz.or@...il.com,
	andy@...yhouse.net, ast@...mgrid.com
Subject: Re: [net-next PATCH v3 00/12] Flow API

On 01/23/15 at 04:53pm, Jiri Pirko wrote:
> Fri, Jan 23, 2015 at 04:34:55PM CET, john.fastabend@...il.com wrote:
> >What I don't have a lot of use for at the moment is an xflows that runs
> >in software? Conceptually it sounds fine but why would I want to mirror
> >hardware limitations into software? And if I make it completely generic
> >it becomes u32 more or less. I could create an optimized version of the
> >hardware dataplane in userspace which sits somewhere between u32 and the
> >other classifiers on flexility and maybe gains some performance but I'm
> >at a loss as to why this is useful. I would rather spend my time getting
> >better performance out of u32 and dropping qdisc_lock completely then
> >writing some partially useful filter for software.
> 
> Well, even software implementation has limitations. Take ovs kernel
> datapath as example. You can use your graphs to describe exactly what
> ovs can handle. And after that you could use xflows api to set it up as
> well as your rocker offload. That to me seems lie a very nice feature to
> have.

What is the value of this? The OVS kernel datapath is already built to
fall back to user space if the kernel datapath does not support a
specific feature.
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