linux-kernel - Re: [patch 2/13] signal/timer/event fds v6

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Message-Id: <200703190045.24605.arnd@arndb.de>
Date:	Mon, 19 Mar 2007 00:45:23 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...sign.ru>
Subject: Re: [patch 2/13] signal/timer/event fds v6 - signalfd core ...

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 <><
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