From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754743AbYL0PyT (ORCPT ); Sat, 27 Dec 2008 10:54:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754121AbYL0PyJ (ORCPT ); Sat, 27 Dec 2008 10:54:09 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:57064 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754082AbYL0PyG (ORCPT ); Sat, 27 Dec 2008 10:54:06 -0500 Date: Sat, 27 Dec 2008 16:53:39 +0100 From: Ingo Molnar To: Brian Gerst Cc: Christoph Lameter , Thomas Gleixner , "H. Peter Anvin" , Jeremy Fitzhardinge , Alexander van Heukelum , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] x86-64: Convert the PDA to percpu. Message-ID: <20081227155339.GA17851@elte.hu> References: <1230052506-5041-1-git-send-email-brgerst@gmail.com> <20081227104123.GH14639@elte.hu> <73c1f2160812270730w249eabb4labaa4fa3bc6a6ddd@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <73c1f2160812270730w249eabb4labaa4fa3bc6a6ddd@mail.gmail.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Brian Gerst wrote: > On Sat, Dec 27, 2008 at 5:41 AM, Ingo Molnar wrote: > > > > (Cc:-ed a few more people who might be interested in this) > > > > * Brian Gerst wrote: > > > >> This patch makes the PDA a normal per-cpu variable, allowing the > >> removal of the special allocator code. %gs still points to the > >> base of the PDA. > >> > >> Tested on a dual-core AMD64 system. > >> > >> Signed-off-by: Brian Gerst > >> --- > >> arch/x86/include/asm/pda.h | 3 -- > >> arch/x86/include/asm/percpu.h | 3 -- > >> arch/x86/include/asm/setup.h | 1 - > >> arch/x86/kernel/cpu/common.c | 6 ++-- > >> arch/x86/kernel/dumpstack_64.c | 8 ++-- > >> arch/x86/kernel/head64.c | 23 +------------ > >> arch/x86/kernel/irq.c | 2 +- > >> arch/x86/kernel/nmi.c | 2 +- > >> arch/x86/kernel/setup_percpu.c | 70 ++++++++-------------------------------- > >> arch/x86/kernel/smpboot.c | 58 +-------------------------------- > >> arch/x86/xen/enlighten.c | 2 +- > >> arch/x86/xen/smp.c | 12 +------ > >> 12 files changed, 27 insertions(+), 163 deletions(-) > > > > the simplification factor is significant. I'm wondering, have you measured > > the code size impact of this on say the defconfig x86 kernel? That will > > generally tell us how much worse optimizations the compiler does under > > this scheme. > > > > Ingo > > > > Patch #1 by itself doesn't change how the PDA is accessed, only how it > is allocated. The text size goes down significantly with patch #1, > but data goes up. Changing the PDA to cacheline-aligned (1a) brings > it back in line. > > text data bss dec hex filename > 7033648 1754476 758508 9546632 91ab88 vmlinux.0 (vanilla 2.6.28) > 7029563 1758428 758508 9546499 91ab03 vmlinux.1 (with patch #1) > 7029563 1754460 758508 9542531 919b83 vmlinux.1a (with patch #1 cache align) > 7036694 1758428 758508 9553630 91c6de vmlinux.3 (with all three patches) > > I think the first patch (with the alignment fix) is a clear win. As for > the other patches, they add about 8 bytes per use of a PDA variable. > cpu_number is used 903 times in this compile, so this is likely the most > extreme example. I have an idea to optimize this particular case > further that I'd like to look at which would lessen the impact. curious, what idea is that? Ingo