netdev - ip_summed setting for TCP pure-ACK packets

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Message-ID: <1289234113.2222.20.camel@achroite.uk.solarflarecom.com>
Date:	Mon, 08 Nov 2010 16:35:13 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Miller <davem@...emloft.net>
Cc:	sf-linux-drivers <linux-net-drivers@...arflare.com>,
	netdev <netdev@...r.kernel.org>
Subject: ip_summed setting for TCP pure-ACK packets

As we discussed at LPC:

Current controllers handled by the sfc driver have a per-queue (rather
than per-packet) option for checksum generation.  Currently pure-ACK
packets sent by TCP have ip_summed == CHECKSUM_NONE and we must send
them on hardware queues with checksum generation disabled.  To support
this, we allocate 2 hardware queues per core TX queue.

To reduce the risk of reordering (and possibly the number of hardware TX
queues required), it would be helpful for TCP to set ip_summed ==
CHECKSUM_PARTIAL on pure-ACK packets when the output device is known to
support checksum generation.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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