Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757543AbXEXJDd (ORCPT ); Thu, 24 May 2007 05:03:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755263AbXEXJDZ (ORCPT ); Thu, 24 May 2007 05:03:25 -0400 Received: from mtagate1.de.ibm.com ([195.212.29.150]:18319 "EHLO mtagate1.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755127AbXEXJDY (ORCPT ); Thu, 24 May 2007 05:03:24 -0400 Subject: Re: [PATCH 1/2] Define new percpu interface for shared data -- version 3 From: Martin Schwidefsky Reply-To: schwidefsky@de.ibm.com To: Ravikiran G Thirumalai Cc: "Yu, Fenghua" , Andrew Morton , "Siddha, Suresh B" , clameter@sgi.com, rmk@arm.linux.org.uk, linux-kernel@vger.kernel.org, heiko.carstens@de.ibm.com In-Reply-To: <20070523185748.GA4072@localhost.localdomain> References: <20070523104946.f279241c.akpm@linux-foundation.org> <79E93560F4A5FD42BB769DAAF8BEF62A01AA8C77@scsmsx411.amr.corp.intel.com> <20070523185748.GA4072@localhost.localdomain> Content-Type: text/plain Organization: IBM Corporation Date: Thu, 24 May 2007 11:03:56 +0200 Message-Id: <1179997436.8070.3.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.10.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1437 Lines: 41 On Wed, 2007-05-23 at 11:57 -0700, Ravikiran G Thirumalai wrote: > > >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) Current git with the patches applied and the default configuration for s390 decreases the section size fof .data.percpu from 0x3e50 to 0x3e00. 0.5% decrease. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. - 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/