Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760015AbXEWS5e (ORCPT ); Wed, 23 May 2007 14:57:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756000AbXEWS50 (ORCPT ); Wed, 23 May 2007 14:57:26 -0400 Received: from byss.tchmachines.com ([208.76.80.75]:57050 "EHLO byss.tchmachines.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755619AbXEWS50 (ORCPT ); Wed, 23 May 2007 14:57:26 -0400 Date: Wed, 23 May 2007 11:57:48 -0700 From: Ravikiran G Thirumalai To: "Yu, Fenghua" Cc: Andrew Morton , "Siddha, Suresh B" , clameter@sgi.com, rmk@arm.linux.org.uk, linux-kernel@vger.kernel.org, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com Subject: Re: [PATCH 1/2] Define new percpu interface for shared data -- version 3 Message-ID: <20070523185748.GA4072@localhost.localdomain> References: <20070523104946.f279241c.akpm@linux-foundation.org> <79E93560F4A5FD42BB769DAAF8BEF62A01AA8C77@scsmsx411.amr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <79E93560F4A5FD42BB769DAAF8BEF62A01AA8C77@scsmsx411.amr.corp.intel.com> User-Agent: Mutt/1.4.2.1i X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - byss.tchmachines.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - scalex86.org X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1300 Lines: 35 On Wed, May 23, 2007 at 11:26:53AM -0700, Yu, Fenghua wrote: > > elements are cacheline aligned. And as such, this differentiates the > local > > only data and remotely accessed data cleanly. > > >OK, but could we please have a concise description of the impact > >of these changes on kernel memory footprint? Increase or decrease? > >And by approximately how much? > > Depending on how linker places percpu data, the patches could > increase or decrease percpu section size. Data from 2.6.21-rc7-mm2: > > On x86 SMP, the section size is increased from 0x7768 to 0x790c. > 1.3% increase. > > On X86-64 SMP, the size is decreased from 0x72d0 to 0x6540. > 11.8% decrease. > > On X86-64 VSMP, the size is increased from 0x72d0 to 0x8340. > 14.3% increase. > > On IA64 SMP, the size is decreased from 0x8370 to 0x7fc0. > 2.8% decrease. Has there been any measurable benefit yet due to tail padding? It would also be interesting to check the wastage/savings on another large cache architecture like S390 (which has a 256 byte cache line) Thanks, Kiran - 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/