Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760291AbYCYVfx (ORCPT ); Tue, 25 Mar 2008 17:35:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754024AbYCYVfo (ORCPT ); Tue, 25 Mar 2008 17:35:44 -0400 Received: from ozlabs.org ([203.10.76.45]:33563 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753626AbYCYVfn (ORCPT ); Tue, 25 Mar 2008 17:35:43 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <18409.28204.539283.566893@cargo.ozlabs.ibm.com> Date: Wed, 26 Mar 2008 08:27:08 +1100 From: Paul Mackerras To: Andi Kleen Cc: David Miller , clameter@sgi.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org, torvalds@linux-foundation.org Subject: Re: larger default page sizes... In-Reply-To: <87wsnrgg9q.fsf@basil.nowhere.org> References: <20080321.145712.198736315.davem@davemloft.net> <20080324.133722.38645342.davem@davemloft.net> <18408.29107.709577.374424@cargo.ozlabs.ibm.com> <87wsnrgg9q.fsf@basil.nowhere.org> X-Mailer: VM 7.19 under Emacs 21.4.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1259 Lines: 30 Andi Kleen writes: > Paul Mackerras writes: > > > > 4kB pages: 444.051s user + 34.406s system time > > 64kB pages: 419.963s user + 16.869s system time > > > > That's nearly 10% faster with 64kB pages -- on a kernel compile. > > Do you have some idea where the improvement mainly comes from? > Is it TLB misses or reduced in kernel overhead? Ok I assume both > play together but which part of the equation is more important? I think that to a first approximation, the improvement in user time (24 seconds) is due to the increased TLB reach and reduced TLB misses, and the improvement in system time (18 seconds) is due to the reduced number of page faults and reductions in other kernel overheads. As Dave Hansen points out, I can separate the two effects by having the kernel use 64k pages at the VM level but 4k pages in the hardware page table, which is easy since we have support for 64k base page size on machines that don't have hardware 64k page support. I'll do that today. Paul. -- 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/