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From: "David Laight" <David.Laight@ACULAB.COM>
To: "Ben Hutchings" <bhutchings@solarflare.com>,
	"David Miller" <davem@davemloft.net>,
	"Heiko Carstens" <heiko.carstens@de.ibm.com>,
	"Geert Uytterhoeven" <geert@linux-m68k.org>
Cc: <linux-net-drivers@solarflare.com>,
	"Linux Kernel Development" <linux-kernel@vger.kernel.org>,
	<linux-s390@vger.kernel.org>, "netdev" <netdev@vger.kernel.org>
Subject: RE: [PATCHv2 net 1/2] sfc: Delete EFX_PAGE_IP_ALIGN, equivalent to NET_IP_ALIGN
Date: Tue, 14 May 2013 09:32:18 +0100	[thread overview]
Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B7235@saturn3.aculab.com> (raw)
In-Reply-To: <1368482311.3305.48.camel@bwh-desktop.uk.solarflarecom.com>

> The two architectures that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> (powerpc and x86) now both define NET_IP_ALIGN as 0, so there is no
> need for this optimisation any more.

Hmmm.... even on x86 there will be a measurable cost
in misaligned accesses - at least for some workloads.

If the DMA is able to write to a mis-aligned buffer and
still perform aligned burst transfers mid-frame then
4n+2 aligning the rx buffer should be a win even on x86.

Note to hardware engineers: add an option to write two
bytes of junk before the rx data :-)

	David


  parent reply	other threads:[~2013-05-14  8:32 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-05-13 21:58 Ben Hutchings
2013-05-13 22:01 ` [PATCHv2 net 2/2] sfc: Reduce RX scatter buffer size, and reduce alignment if appropriate Ben Hutchings
2013-05-14  7:09   ` Geert Uytterhoeven
2013-05-14 18:32   ` David Miller
2013-07-23 20:19   ` Ben Hutchings
2013-05-14  8:32 ` David Laight [this message]
2013-05-14 13:48   ` [PATCHv2 net 1/2] sfc: Delete EFX_PAGE_IP_ALIGN, equivalent to NET_IP_ALIGN Ben Hutchings
2013-05-14 18:32 ` David Miller

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