netdev - RE: Flows! Offload them.

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Date:	Sun, 1 Mar 2015 09:36:43 +0000
From:	"Arad, Ronen" <ronen.arad@...el.com>
To:	Thomas Graf <tgraf@...g.ch>, Neil Horman <nhorman@...driver.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	Simon Horman <simon.horman@...ronome.com>,
	"Fastabend, John R" <john.r.fastabend@...el.com>,
	Jiri Pirko <jiri@...nulli.us>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"andy@...yhouse.net" <andy@...yhouse.net>,
	"dborkman@...hat.com" <dborkman@...hat.com>,
	"ogerlitz@...lanox.com" <ogerlitz@...lanox.com>,
	"jesse@...ira.com" <jesse@...ira.com>,
	"jpettit@...ira.com" <jpettit@...ira.com>,
	"joestringer@...ira.com" <joestringer@...ira.com>,
	"jhs@...atatu.com" <jhs@...atatu.com>,
	"sfeldma@...il.com" <sfeldma@...il.com>,
	"f.fainelli@...il.com" <f.fainelli@...il.com>,
	"roopa@...ulusnetworks.com" <roopa@...ulusnetworks.com>,
	"linville@...driver.com" <linville@...driver.com>,
	"shrijeet@...il.com" <shrijeet@...il.com>,
	"gospo@...ulusnetworks.com" <gospo@...ulusnetworks.com>,
	"bcrl@...ck.org" <bcrl@...ck.org>
Subject: RE: Flows! Offload them.



>-----Original Message-----
>From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org] On
>Behalf Of Thomas Graf
>Sent: Friday, February 27, 2015 12:42 AM
>To: Neil Horman
>Cc: Simon Horman; Fastabend, John R; Jiri Pirko; netdev@...r.kernel.org;
>davem@...emloft.net; andy@...yhouse.net; dborkman@...hat.com;
>ogerlitz@...lanox.com; jesse@...ira.com; jpettit@...ira.com;
>joestringer@...ira.com; jhs@...atatu.com; sfeldma@...il.com;
>f.fainelli@...il.com; roopa@...ulusnetworks.com; linville@...driver.com;
>shrijeet@...il.com; gospo@...ulusnetworks.com; bcrl@...ck.org
>Subject: Re: Flows! Offload them.
>
>Blind random offload of some packets is better than nothing but knowing
>and having control over which packets are offloaded is essential. You
>typically don't want to randomly give one flow priority over another ;-)
>Some software CPUs might not be able to handle the load. I know what
>you mean though and as long as we allow to disable and overwrite this
>behaviour we are good.
>

Random offloading of flows does not preserve policy in general.
For example let's consider two flows A.B.C.0/24 and A.B.C.D with the more
specific rule has higher priority.
If only the first rule is offloaded to HW, packets matched by the second
rule will not be processed as expected by the user.
Deciding which flow could be offloaded is an optimization decision that
is better handled outside of the kernel. 
  
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