From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753203Ab2A3HNv (ORCPT ); Mon, 30 Jan 2012 02:13:51 -0500 Received: from MAIL.13thfloor.at ([213.145.232.33]:34065 "EHLO MAIL.13thfloor.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751288Ab2A3HNu (ORCPT ); Mon, 30 Jan 2012 02:13:50 -0500 Date: Mon, 30 Jan 2012 08:13:47 +0100 From: Herbert Poetzl To: Shaohua Li Cc: Wu Fengguang , Eric Dumazet , Andrew Morton , LKML , Jens Axboe , Tejun Heo Subject: Re: Bad SSD performance with recent kernels Message-ID: <20120130071346.GM29272@MAIL.13thfloor.at> Mail-Followup-To: Shaohua Li , Wu Fengguang , Eric Dumazet , Andrew Morton , LKML , Jens Axboe , Tejun Heo 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> <1327842831.2718.2.camel@edumazet-laptop> <20120129161058.GA13156@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 30, 2012 at 11:17:38AM +0800, Shaohua Li wrote: > 2012/1/30 Wu Fengguang : >> On Sun, Jan 29, 2012 at 02:13:51PM +0100, Eric Dumazet wrote: >>> 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 >> Interesting. Here are my test results: >> root@lkp-nex04 /home/wfg# echo 3 >/proc/sys/vm/drop_caches ;dd if=/dev/sda of=/dev/null bs=128k count=32768 >> 32768+0 records in >> 32768+0 records out >> 4294967296 bytes (4.3 GB) copied, 19.0121 s, 226 MB/s >> root@lkp-nex04 /home/wfg# echo 3 >/proc/sys/vm/drop_caches ;dd if=/dev/sda of=/dev/null bs=2M count=2048 >> 2048+0 records in >> 2048+0 records out >> 4294967296 bytes (4.3 GB) copied, 19.0214 s, 226 MB/s >> Maybe the /dev/sda performance bug on your machine is sensitive to timing? > I got similar result: > 128k: 224M/s > 1M: 182M/s > 1M block size is slow, I guess it's CPU related. > And as for the big regression with newer kernel than 2.6.38, > please check if idle=poll helps. CPU idle dramatically impacts > disk performance and even latest cpuidle governor doesn't help > for some CPUs. here are the tests with idle=poll and after switching to 128k (instead of 1M) blocksize (same amount of data transferred) kernel ------------ read /dev/sda ------------- --- noop --- - deadline - ---- cfs --- [MB/s] %CPU [MB/s] %CPU [MB/s] %CPU -------------------------------------------------- 3.2.2 45.82 3.7 44.85 3.6 45.04 3.4 3.2.2i 45.59 2.3 51.78 2.6 46.03 2.2 3.2.2i128 250.24 20.9 252.68 21.3 250.00 21.6 kernel -- write --- ------------------read ----------------- --- noop --- --- noop --- - deadline - ---- cfs --- [MB/s] %CPU [MB/s] %CPU [MB/s] %CPU [MB/s] %CPU ---------------------------------------------------------------- 3.2.2 270.95 42.6 162.36 9.9 162.63 9.9 162.65 10.1 3.2.2i 269.10 41.4 170.82 6.6 171.20 6.6 170.91 6.7 3.2.2i128 270.38 67.7 162.35 10.2 163.01 10.3 162.34 10.7 HTH, Herbert > Thanks, > Shaohua