linux-kernel - Re: [PATCH/RFC v2] introduce ARCH_CAN_UNALIGNED

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Message-ID: <20080320220348.GC1330@tuxdriver.com>
Date:	Thu, 20 Mar 2008 18:03:48 -0400
From:	"John W. Linville" <linville@...driver.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	David Miller <davem@...emloft.net>, sam@...nborg.org,
	dsd@...too.org, linux-kernel@...r.kernel.org,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH/RFC v2] introduce ARCH_CAN_UNALIGNED_ACCESS Kconfig
	symbol

On Thu, Mar 20, 2008 at 10:21:46PM +0100, Johannes Berg wrote:
> 
> > I think you're semantically testing the wrong thing.
> > 
> > It's not if unaligned accesses are supported, it's if they are
> > efficient enough or not.
> > 
> > For example, sparc64 fully handles unaligned accesses but taking the
> > trap to fix it up is slow.  So sparc64 "can" handle unaligned
> > accesses, but whether we want to set this symbol or not is another
> > matter.
> 
> Yeah, good point. Should I rename it to HAVE_EFFICIENT_UNALIGNED_ACCESS
> or similar? Or have it defined as some sort of number so you can make
> actually make tradeoffs? Like Dave Woodhouse suggested at some point to
> have get_unaligned() take an argument that indicates the probability...

Ugh...that sounds like premature optimization to me...

While I think Dave has a point, I don't think you should labor the word
choice too much.  Try to document it as clearly as possible and hope
for the best -- I hear that the arch maintainers are top notch! :-)

John

-- 
John W. Linville
linville@...driver.com
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