Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933363AbZDJJV0 (ORCPT ); Fri, 10 Apr 2009 05:21:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755182AbZDJJVQ (ORCPT ); Fri, 10 Apr 2009 05:21:16 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:55430 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755264AbZDJJVP (ORCPT ); Fri, 10 Apr 2009 05:21:15 -0400 Date: Fri, 10 Apr 2009 11:19:31 +0200 From: Ingo Molnar To: Matt Helsley , Tejun Heo , Jeremy Fitzhardinge Cc: Alexey Dobriyan , akpm@linux-foundation.org, containers@lists.linux-foundation.org, xemul@parallels.com, linux-kernel@vger.kernel.org, dave@linux.vnet.ibm.com, hch@infradead.org, torvalds@linux-foundation.org Subject: Re: [PATCH 09/30] x86_64: ifdef out struct thread_struct::ip Message-ID: <20090410091931.GF17962@elte.hu> References: <20090410023522.GJ27788@x200.localdomain> <20090410035328.GB29496@us.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090410035328.GB29496@us.ibm.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 Content-Length: 1893 Lines: 64 * Matt Helsley wrote: > On Fri, Apr 10, 2009 at 06:35:22AM +0400, Alexey Dobriyan wrote: > > struct thread_struct::ip isn't used on x86_64, struct pt_regs::ip is used > > instead. > > > > kgdb should be reading 0, but I can't check it. > > > > Signed-off-by: Alexey Dobriyan > > --- > > > > arch/x86/include/asm/processor.h | 2 ++ > > arch/x86/kernel/kgdb.c | 2 +- > > 2 files changed, 3 insertions(+), 1 deletion(-) > > > > --- a/arch/x86/include/asm/processor.h > > +++ b/arch/x86/include/asm/processor.h > > @@ -421,7 +421,9 @@ struct thread_struct { > > unsigned short fsindex; > > unsigned short gsindex; > > #endif > > +#ifdef CONFIG_X86_32 > > unsigned long ip; > > +#endif > > #ifdef CONFIG_X86_64 > > unsigned long fs; > > #endif > > Do these make struct thread_struct behave better in cachelines > (smaller, less aliasing)? Can we really fit more in the slab du > jour? > > Otherwise it seems like we're littering these structs with #ifdefs > and not really saving anything. [...] Removing fields always saves memory (even if it does not show up currently due to allocators cache-aligning sizes). But the #ifdef ugliness is a real worry. > [...] If these #ifdefs don't save any > space why not just put in a comment: > > > unsigned long ip; /* Used only on i386 */ Yes. > Or maybe even: > > union { > unsigned long ip; /* Used only on i386 */ > unsigned long fs; /* Used only on x86_64 */ > }; Maybe. If this ever gets misunderstood somewhere in platform code we will get ugly failure modes and zero compiler help. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/