From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752741Ab2A2NOL (ORCPT ); Sun, 29 Jan 2012 08:14:11 -0500 Received: from mail-we0-f174.google.com ([74.125.82.174]:40971 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752134Ab2A2NOJ (ORCPT ); Sun, 29 Jan 2012 08:14:09 -0500 Message-ID: <1327842831.2718.2.camel@edumazet-laptop> Subject: Re: Bad SSD performance with recent kernels From: Eric Dumazet To: Wu Fengguang Cc: Herbert Poetzl , Andrew Morton , LKML , Jens Axboe , Tejun Heo Date: Sun, 29 Jan 2012 14:13:51 +0100 In-Reply-To: <20120129111645.GA5839@localhost> References: <20120127060034.GG29272@MAIL.13thfloor.at> <20120128125108.GA9661@localhost> <1327757611.7199.6.camel@edumazet-laptop> <20120129055917.GB8513@localhost> <1327831380.14602.6.camel@edumazet-laptop> <20120129111645.GA5839@localhost> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.2- Content-Transfer-Encoding: 8bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le dimanche 29 janvier 2012 à 19:16 +0800, Wu Fengguang a écrit : > Note that as long as buffered read(2) is used, it makes almost no > difference (well, at least for now) to do "dd bs=128k" or "dd bs=2MB": > the 128kb readahead size will be used underneath to submit read IO. > Hmm... # echo 3 >/proc/sys/vm/drop_caches ;dd if=/dev/sda of=/dev/null bs=128k count=32768 32768+0 enregistrements lus 32768+0 enregistrements écrits 4294967296 octets (4,3 GB) copiés, 20,7718 s, 207 MB/s # echo 3 >/proc/sys/vm/drop_caches ;dd if=/dev/sda of=/dev/null bs=2M count=2048 2048+0 enregistrements lus 2048+0 enregistrements écrits 4294967296 octets (4,3 GB) copiés, 27,7824 s, 155 MB/s