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From: Arnd Bergmann <arnd@arndb.de>
To: Davide Libenzi <davidel@xmailserver.org>
Subject: Re: [patch 2/13] signal/timer/event fds v6 - signalfd core ...
Date: Mon, 19 Mar 2007 00:45:23 +0100
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On Sunday 18 March 2007, Davide Libenzi wrote:
> bah, __put_user is basically a move, so I don't think that efficency would 
> be that different (assuming that it'd matter in this case). The only thing 
> many __put_user do, is increase the exception table sizes.

The cost of user access functions varies a lot depending on the
architectures. Those platforms with a 4G/4G split e.g. need to do more
than a simple move, and for s390 it may even come down to an indirect
function call, which incurs significant register pressure.

	Arnd <><