Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 10 Feb 2003 09:40:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 10 Feb 2003 09:40:26 -0500 Received: from denise.shiny.it ([194.20.232.1]:56228 "EHLO denise.shiny.it") by vger.kernel.org with ESMTP id ; Mon, 10 Feb 2003 09:40:25 -0500 Message-ID: X-Mailer: XFMail 1.4.7 on Linux X-Priority: 3 (Normal) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8bit MIME-Version: 1.0 In-Reply-To: <20030210034808.7441d611.akpm@digeo.com> Date: Mon, 10 Feb 2003 15:49:59 +0100 (CET) From: Giuliano Pochini To: Andrew Morton Subject: Re: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2. Cc: linux-kernel@vger.kernel.org, riel@conectiva.com.br, Andrea Arcangeli Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1235 Lines: 26 >> You can wait 10 minutes and still such command can't grow. This is why >> claiming anticipatory scheduling can decrease the need for readahead >> doesn't make much sense to me, there are important things you just can't >> achieve by only waiting. >> > > The anticipatory scheduler can easily permit 512k of reading before seeking > away to another file. In fact it can allow much more, without requiring that > readhead be cranked up. IMHO anticipatory scheduling and readahead address different problems. RA is simpler and cheaper. Reading a few more KB comes almost for free and that helps a lot sequential reads. AS is useful for random i/o (fs metadata, executables, ...), but it wastes time if the timer expires, or if the new request wants data which is far away the previous one. AS is useful for sequential reads too, but only if the application reads large chunks of data, otherwise RA is better. I we need both RA and AS to address the largest variety of workloads. Bye. - 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/