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

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Message-ID: <49C53CC0.5060303@zytor.com>
Date:	Sat, 21 Mar 2009 12:15:12 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Dan Williams <dan.j.williams@...el.com>
CC:	Ilya Yanok <yanok@...raft.com>,
	"H. Peter Anvin" <h.peter.anvin@...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

Dan Williams wrote:
>>
>> 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.
> 
> Understood.  However this routine also needs to cover the non-generic
> and non-constant case where we have a separate coefficient per
> element.  I suppose it could scan the coefficient list to see if it
> can bypass the 2-dimensional lookup multiply.  At the very least we
> need something like the following, because async_pq is really only a
> helper routine for async_r6recov.c which knows how to avoid the
> synchronous path.
> 

Why does it?  I don't see why you'd need to cover the vector-vector case
at all, since it doesn't appear anywhere in the algorithms.  Certainly
going backwards from a vector-vector set to derive if you can do a
scalar-vector multiply when you should have known that in the first
place is not really useful.

> 
> Looking closer, the only other caller, async_pq_zero_sum, can be
> deleted because it has no users.  So async_pq can become a static
> routine in async_r6recov.
> 

That's another issue entirely, of course :)

	-hpa

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

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