From owner-freebsd-stable@FreeBSD.ORG Thu Dec 21 15:35:17 2006 Return-Path: X-Original-To: freebsd-stable@freebsd.org Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id C59B116A415 for ; Thu, 21 Dec 2006 15:35:17 +0000 (UTC) (envelope-from pieter@degoeje.nl) Received: from smtp.utwente.nl (smtp1.utsp.utwente.nl [130.89.2.8]) by mx1.freebsd.org (Postfix) with ESMTP id 4FC0813C434 for ; Thu, 21 Dec 2006 15:35:17 +0000 (UTC) (envelope-from pieter@degoeje.nl) Received: from nox.student.utwente.nl (nox.student.utwente.nl [130.89.165.91]) by smtp.utwente.nl (8.12.10/SuSE Linux 0.7) with ESMTP id kBLFK3Lr025718; Thu, 21 Dec 2006 16:20:04 +0100 From: Pieter de Goeje To: Mark Kirkwood Date: Thu, 21 Dec 2006 16:20:03 +0100 User-Agent: KMail/1.9.4 References: <45888C68.10305@paradise.net.nz> <200612201536.25497.pieter@degoeje.nl> <4589A921.90002@paradise.net.nz> In-Reply-To: <4589A921.90002@paradise.net.nz> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200612211620.03590.pieter@degoeje.nl> X-UTwente-MailScanner-Information: Scanned by MailScanner. Contact helpdesk@ITBE.utwente.nl for more information. X-UTwente-MailScanner: Found to be clean X-UTwente-MailScanner-From: pieter@degoeje.nl X-Spam-Status: No Cc: freebsd-stable@freebsd.org Subject: Re: Cached file read performance with 6.2-PRERELEASE X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 21 Dec 2006 15:35:17 -0000 On Wednesday 20 December 2006 22:20, Mark Kirkwood wrote: > Pieter de Goeje wrote: > > On Wednesday 20 December 2006 11:38, Mark Kirkwood wrote: > >> In fact if you note that the PIII HW *can* actually do 700MB/s, it > >> suggests that your HW is capable of considerably more than 900MB/s - > >> given that opteron's have excellent cpu to memory bandwidth, and the > >> speed of your memory! > > > > Indeed! > > Copying /dev/zero to /dev/null yields more than 5GB/sec on a simple 2Ghz > > Athlon64. It imagine there are quite a few extra things done when copying On second thought, this is wrong because /dev/zero isn't a real block of memory so these results say nothing about memory I/O speed because all data is in (cpu) cache. > > a file from cache, because I can only manage to get one fifth (~1GB/sec) > > of the theoretical speed. (this is with a file that fills more than half > > of all memory) > > > > Note that linux seems to play tricks (zero copy?) when doing dd > > if=/dev/zero of=/dev/null, because you can reach speeds which are way > > above the theoretical maximum. (30GB/sec on a P4 1,6Ghz ??? no way) > > > > In the context of databases, I think the speeds are limited by the > > processing done on the data, as long as the read speed stays above a > > certain limit. > > Yeah - typically it is creating tuples out of the blocks/pages just > read, so for a big memory scan CPU appears to be the limiting factor! > > > It would be more interesting to see how random access to a (cached) file > > performs in Linux vs FreeBSD, which seems a more logical pattern for a > > database. > > Agreed, and good point, I'll knock up a simple program to do random > and/or sequential access of a file and see what we get! I'll check 'em out :) Cheers, Pieter