linux-kernel - Re: [PATCH 06/13] async_tx: add support for asynchronous GF multiplication

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Message-ID: <49C45159.8020503@zytor.com>
Date:	Fri, 20 Mar 2009 19:30:49 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ilya Yanok <yanok@...raft.com>
CC:	"H. Peter Anvin" <h.peter.anvin@...el.com>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"neilb@...e.de" <neilb@...e.de>,
	"Sosnowski, Maciej" <maciej.sosnowski@...el.com>,
	Yuri Tikhonov <yur@...raft.com>
Subject: Re: [PATCH 06/13] async_tx: add support for asynchronous GF 	multiplication

Ilya Yanok wrote:
> 
> async_gen_syndrome() takes element of GF^n(256) and returns result of
> scalar multiplication of it with constant ({01}, {02}, {02}^2, ...,
> {02}^n) vector.

For any n (which would mean any GF field)?  In that case, that is
generic scalar-vector multiplication...

> async_pq() takes two vectors from GF^n(256) and returns their scalar
> multiplication.
> 
> We need async_pq() function if we want to offload D_x = A * (P + P_{xy})
> + B * (Q + Q_{xy}) part of DD recovery and D_x = (Q + Q_x) * g^{-x} part
> of DP recovery.


No, you don't.  A and B (and g^{-x}) are scalars, meaning they're the
same for every element.  This is simpler to do.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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