Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965392AbXATWAs (ORCPT ); Sat, 20 Jan 2007 17:00:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965401AbXATWAs (ORCPT ); Sat, 20 Jan 2007 17:00:48 -0500 Received: from [139.30.44.16] ([139.30.44.16]:3994 "EHLO gockel.physik3.uni-rostock.de" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S965392AbXATWAr (ORCPT ); Sat, 20 Jan 2007 17:00:47 -0500 Date: Sat, 20 Jan 2007 23:00:46 +0100 (CET) From: Tim Schmielau To: Sunil Naidu cc: =?UTF-8?Q?Ismail_D=C3=B6nm?= , Willy Tarreau , lkml Subject: Re: Abysmal disk performance, how to debug? In-Reply-To: <8355959a0701201312r9a3aac4ufd151ca18ef7e64e@mail.gmail.com> Message-ID: References: <200701201920.54620.ismail@pardus.org.tr> <20070120174503.GZ24090@1wt.eu> <200701201952.54714.ismail@pardus.org.tr> <8355959a0701201312r9a3aac4ufd151ca18ef7e64e@mail.gmail.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2270 Lines: 72 On Sun, 21 Jan 2007, Sunil Naidu wrote: > On 1/21/07, Tim Schmielau wrote: > > > > Note that these dd "benchmarks" are completely bogus, because the data > > doesn't actually get written to disk in that time. For some enlightening > > data, try > > > > time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024; time sync > > > > The dd returns as soon as all data could be buffered in RAM. Only sync > > will show how long it takes to actually write out the data to disk. > > also explains why you see better results is writeout starts earlier. > > I am still getting better I feel: Yes. You have a faster Disk that writes about 45 MB/s. But I am not sure I understand what you want to know? > [sukhoi@Typhoon ~]$ time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024; time > sync > 1024+0 records in > 1024+0 records out > 1073741824 bytes (1.1 GB) copied, 19.5007 seconds, 55.1 MB/s > > real 0m20.439s > user 0m0.004s > sys 0m4.535s > > real 0m4.625s > user 0m0.000s > sys 0m0.125s > > > [sukhoi@Typhoon ~]$ time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024 | sync > 1024+0 records in > 1024+0 records out > 1073741824 bytes (1.1 GB) copied, 20.8707 seconds, 51.4 MB/s > > real 0m22.449s > user 0m0.002s > sys 0m4.922s > > > Linux used here is not 2.6.20-rc5, but it's a FC6 2.6.19 binary. Shall > post the results with 2.6.20-rc5. > > BTW, does the results vary with a customized kernel (configured w.r.t > Processor & Hardware) than a generic kernel like FC6? I'd guess the kernel won't make much of a difference as the time is mostly determined by RAM and disk speeds. > Are there any other such test cases? Well, what do you want to find out? Anyways, I am in no way expert in the field of benchmarking. Note to Willy: I finally noticed my logic actually was not flawed. I stated why dd would report approximately doubled throughputs with buffering, while you argued why the total elapsed time would not change much. Time to go to bed now... Tim - 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/