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Subject: Re: Unmapped buffers: to be merged in several days
From: Jim Harris <jimharris@freebsd.org>
To: Konstantin Belousov <kostikbel@gmail.com>
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Cc: Dag-Erling Sm??rgrav <des@des.no>, Lev Serebryakov <lev@serebryakov.spb.ru>,
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On Mon, Mar 11, 2013 at 2:11 PM, Konstantin Belousov <kostikbel@gmail.com>wrote:

> FWIW, I tried to get an Intel documentation for IOAT engine which should
> allow to perform the XOR checksumming of the unmapped buffers, suitable
> for e.g. hardware-assisted software raid5, but did not succeeded.
>

Please note that XOR checksumming support only exists in the
E5-1600/2400/2600/4600 series (Sandy Bridge Xeon) and C5500/C3500 series
(Jasper Forest - based on Nehalem Xeon) processors.  The SNB Xeon series
EDS section for IOAT isn't public, but the Jasper Forest datasheet volume 2
does contain the register interfaces.  See sections 3.9 and section 3.10.
The ioat HW interface for XOR is the same for both series save for some
delta in errata.

http://www.intel.com/content/dam/www/public/us/en/documents/datasheets/xeon-c5500-c3500-datasheet-vol-2.pdf

Also note there is an ioat driver (DMA operations only) on the
user/jimharris/ioat branch in the FreeBSD SVN repo.  The Linux ioat driver
with XOR support is dual-licensed BSD/GPL.

Regards,

-Jim