Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267798AbUIXFAs (ORCPT ); Fri, 24 Sep 2004 01:00:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267804AbUIXFAs (ORCPT ); Fri, 24 Sep 2004 01:00:48 -0400 Received: from mail04.syd.optusnet.com.au ([211.29.132.185]:2200 "EHLO mail04.syd.optusnet.com.au") by vger.kernel.org with ESMTP id S267798AbUIXFAo (ORCPT ); Fri, 24 Sep 2004 01:00:44 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <16723.43493.796084.90914@wombat.chubb.wattle.id.au> Date: Fri, 24 Sep 2004 15:00:21 +1000 From: Peter Chubb To: Andrew Morton Cc: Steven Pratt , linux-kernel@vger.kernel.org, linux-fs-devel@vger.kernel.org Subject: Re: [PATCH/RFC] Simplified Readahead In-Reply-To: <372479081@toto.iv> X-Mailer: VM 7.17 under 21.4 (patch 15) "Security Through Obscurity" XEmacs Lucid Comments: Hyperbole mail buttons accepted, v04.18. X-Face: GgFg(Z>fx((4\32hvXq<)|jndSniCH~~$D)Ka:P@e@JR1P%Vr}EwUdfwf-4j\rUs#JR{'h# !]])6%Jh~b$VA|ALhnpPiHu[-x~@<"@Iv&|%R)Fq[[,(&Z'O)Q)xCqe1\M[F8#9l8~}#u$S$Rm`S9% \'T@`:&8>Sb*c5d'=eDYI&GF`+t[LfDH="MP5rwOO]w>ALi7'=QJHz&y&C&TE_3j! Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2571 Lines: 54 >>>>> "Andrew" == Andrew Morton writes: Andrew> Steven Pratt wrote: >> The readahead code has undergone many changes in the 2.6 kernel >> and the current implementation is in my opinion obtuse and hard to >> maintain. Andrew> It did get a bit ugly - it was intially designed to handle Andrew> pagefault readaround and perhaps could be further simplified Andrew> as we're now doing that independently. If you're coding up new readahead schemes, it may be worth taking into account Papathanasiou and Scott, `Energy Efficient Prefetching and Caching' ( http://www.usenix.org/events/usenix04/tech/general/papathanasiou/papathanasiou_html/index.html ) which describes tuning of readahead for optimum disk energy usage, while not compromising performance. Here's the abstract: Traditional disk management strategies--prefetching and caching in particular--are designed to maximize performance. In mobile systems they conflict with strategies that attempt to save energy by powering down the disk when it is idle. We present new rules for prefetching and caching that maximize power-down opportunities (without performance loss) by creating an access pattern characterized by intense bursts of activity separated by long idle times. We also describe an automatic system that monitors past application behavior in order to generate appropriate prefetching hints, and a general system of kernel enhancements that coordinate I/O activity across all running applications. We have implemented our system in the Linux kernel, and have measured its performance and energy consumption via physical instrumentation of a running laptop. We describe our implementation and present quantitative results. For workloads including a mix of sequential access to large files (multimedia), concurrent access to large numbers of files (compilation), and random access to large files (speech recognition), we report disk energy savings of 60-80%, with negligible loss in throughput or interactive responsiveness. -- Dr Peter Chubb http://www.gelato.unsw.edu.au peterc AT gelato.unsw.edu.au The technical we do immediately, the political takes *forever* - 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/