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

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Message-ID: <Pine.LNX.4.64.0703181720410.5482@alien.or.mcafeemobile.com>
Date:	Sun, 18 Mar 2007 17:22:48 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Arnd Bergmann <arnd@...db.de>
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 Mon, 19 Mar 2007, Arnd Bergmann wrote:

> 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.

Heh, I'd like ppl to agree on this, because I clearly remember in having 
an argoument with Andrew for the same thing, where I was doing stack setup 
plus copy_to_user() ;)



- Davide


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