Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965382AbXATUVe (ORCPT ); Sat, 20 Jan 2007 15:21:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965381AbXATUVe (ORCPT ); Sat, 20 Jan 2007 15:21:34 -0500 Received: from [139.30.44.16] ([139.30.44.16]:26317 "EHLO gockel.physik3.uni-rostock.de" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S965377AbXATUVd (ORCPT ); Sat, 20 Jan 2007 15:21:33 -0500 Date: Sat, 20 Jan 2007 21:21:32 +0100 (CET) From: Tim Schmielau To: Ismail =?utf-8?q?D=C3=B6nmez?= cc: Willy Tarreau , linux-kernel@vger.kernel.org Subject: Re: Abysmal disk performance, how to debug? In-Reply-To: <200701202216.16637.ismail@pardus.org.tr> Message-ID: References: <200701201920.54620.ismail@pardus.org.tr> <200701201952.54714.ismail@pardus.org.tr> <200701202216.16637.ismail@pardus.org.tr> MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="512430124-2011241176-1169324492=:23674" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1901 Lines: 54 This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --512430124-2011241176-1169324492=:23674 Content-Type: TEXT/PLAIN; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE On Sat, 20 Jan 2007, Ismail D=C3=B6nmez wrote: > 20 Oca 2007 Cts 22:10 tarihinde, Tim Schmielau =C5=9Funlar=C4=B1 yazm=C4= =B1=C5=9Ft=C4=B1:=20 > > > > Note that these dd "benchmarks" are completely bogus, because the data= =3D20 > > doesn't actually get written to disk in that time. For some enlightenin= g=3D20 > > data, try > > > > time dd if=3D3D/dev/zero of=3D3D/tmp/1GB bs=3D3D1M count=3D3D1024; ti= me sync ^^^^ > > > > The dd returns as soon as all data could be buffered in RAM. Only sync= =3D20 > > 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. >=20 > Still not that bad: >=20 > [~]> time dd if=3D/dev/zero of=3D/tmp/1GB bs=3D1M count=3D1024;sync > 1024+0 records in > 1024+0 records out > 1073741824 bytes (1,1 GB) copied, 53,3194 s, 20,1 MB/s >=20 > real 0m53.517s > user 0m0.003s > sys 0m3.193s >=20 That's not the point, you still measured the same as before (but you might= =20 have noticed that, after printing the results, the shell prompt took some= =20 time to appear). I appended "time sync" to the command to show that=20 (depending on the amount of available memory) actually most of the time=20 is spent in the "sync", not the "dd". Tim --512430124-2011241176-1169324492=:23674-- - 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/