From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751464AbWFPPka (ORCPT ); Fri, 16 Jun 2006 11:40:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751459AbWFPPka (ORCPT ); Fri, 16 Jun 2006 11:40:30 -0400 Received: from mx2.suse.de ([195.135.220.15]:42972 "EHLO mx2.suse.de") by vger.kernel.org with ESMTP id S1751462AbWFPPk1 (ORCPT ); Fri, 16 Jun 2006 11:40:27 -0400 From: Andi Kleen To: Brent Casavant Subject: Re: FOR REVIEW: New x86-64 vsyscall vgetcpu() Date: Fri, 16 Jun 2006 17:40:18 +0200 User-Agent: KMail/1.9.3 Cc: Zoltan Menyhart , Jes Sorensen , Tony Luck , discuss@x86-64.org, linux-kernel@vger.kernel.org, libc-alpha@sourceware.org, vojtech@suse.cz, linux-ia64@vger.kernel.org References: <200606140942.31150.ak@suse.de> <200606161656.40930.ak@suse.de> <20060616102516.A91827@pkunk.americas.sgi.com> In-Reply-To: <20060616102516.A91827@pkunk.americas.sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200606161740.18611.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > To this last point, it might be more reasonable to map in a page that > contained a new structure with a stable ABI, which mirrored some of > the task_struct information, and likely other useful information as > needs are identified in the future. In any case, it would be hard > to beat a single memory read for performance. That would mean making the context switch and possibly other things slower. In general you would need to make a very good case first that all this complexity is worth it. > Cache-coloring and kernel bookkeeping effects could be minimized if this > was provided as an mmaped page from a device driver, used only by > applications which care. I don't see what difference that would make. You would still have the fixed offset problem and doing things on demand often tends to be even more complex. -Andi (who thinks these proposals all sound very messy)