From: Ben Hutchings <bhutchings@solarflare.com>
Date: Tue, 22 Feb 2011 17:26:10 +0000 (+0000)
Subject: sfc: Use write-combining to reduce TX latency
X-Git-Tag: v2.6.39-rc1~468^2~128^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=65f0b417dee94f779ce9b77102b7d73c93723b39;p=pandora-kernel.git

sfc: Use write-combining to reduce TX latency

Based on work by Neil Turton <nturton@solarflare.com> and
Kieran Mansley <kmansley@solarflare.com>.

The BIU has now been verified to handle 3- and 4-dword writes within a
single 128-bit register correctly.  This means we can enable write-
combining and only insert write barriers between writes to distinct
registers.

This has been observed to save about 0.5 us when pushing a TX
descriptor to an empty TX queue.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
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