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

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Message-Id: <1206048106.16475.161.camel@johannes.berg>
Date:	Thu, 20 Mar 2008 22:21:46 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	David Miller <davem@...emloft.net>
Cc:	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


> 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...

johannes

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