linux-kernel - Re: [PATCH 1/1] lro: Generic Large Receive Offload for TCP traffic

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Message-ID: <20070803134150.GH19344@lazybastard.org>
Date:	Fri, 3 Aug 2007 15:41:50 +0200
From:	Jörn Engel <joern@...fs.org>
To:	Jan-Bernd Themann <ossthema@...ibm.com>
Cc:	David Miller <davem@...emloft.net>,
	Christoph Raisch <raisch@...ibm.com>,
	Jan-Bernd Themann <themann@...ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ppc <linuxppc-dev@...abs.org>,
	Marcus Eder <meder@...ibm.com>,
	Thomas Klein <tklein@...ibm.com>,
	netdev <netdev@...r.kernel.org>,
	Andrew Gallatin <gallatin@...i.com>,
	Jeff Garzik <jeff@...zik.org>,
	Stefan Roscher <stefan.roscher@...ibm.com>
Subject: Re: [PATCH 1/1] lro: Generic Large Receive Offload for TCP traffic

On Fri, 3 August 2007 14:41:19 +0200, Jan-Bernd Themann wrote:
> 
> This patch provides generic Large Receive Offload (LRO) functionality
> for IPv4/TCP traffic.
> 
> LRO combines received tcp packets to a single larger tcp packet and 
> passes them then to the network stack in order to increase performance
> (throughput). The interface supports two modes: Drivers can either pass
> SKBs or fragment lists to the LRO engine. 

Maybe this is a stupid question, but why is LRO done at the device
driver level?

If it is a unversal performance benefit, I would have expected it to be
done generically, i.e. have all packets moved into network layer pass
through LRO instead.

> +void lro_flush_pkt(struct net_lro_mgr *lro_mgr,
> +		   struct iphdr *iph, struct tcphdr *tcph);

In particular this bit looks like it should be driven by a timeout,
which would be settable via /proc/sys/net/core/lro_timeout or similar.

Jörn

-- 
Rules of Optimization:
Rule 1: Don't do it.
Rule 2 (for experts only): Don't do it yet.
-- M.A. Jackson
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