From owner-freebsd-performance@FreeBSD.ORG Mon May 9 12:14:27 2005 Return-Path: Delivered-To: freebsd-performance@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 16C4616A4E7; Mon, 9 May 2005 12:14:27 +0000 (GMT) Received: from critter.freebsd.dk (0x535c0e2a.sgnxx1.adsl-dhcp.tele.dk [83.92.14.42]) by mx1.FreeBSD.org (Postfix) with ESMTP id E3CDF43D6B; Mon, 9 May 2005 12:14:25 +0000 (GMT) (envelope-from phk@critter.freebsd.dk) Received: from critter.freebsd.dk (localhost [127.0.0.1]) by critter.freebsd.dk (8.13.3/8.13.3) with ESMTP id j49CEEfb000692; Mon, 9 May 2005 14:14:17 +0200 (CEST) (envelope-from phk@critter.freebsd.dk) To: Bruce Evans From: "Poul-Henning Kamp" In-Reply-To: Your message of "Mon, 09 May 2005 21:11:16 +1000." <20050509203849.J20942@delplex.bde.org> Date: Mon, 09 May 2005 14:14:14 +0200 Message-ID: <691.1115640854@critter.freebsd.dk> Sender: phk@critter.freebsd.dk cc: Scott Long cc: Petri Helenius cc: Robert Watson cc: Steven Hartland cc: freebsd-performance@FreeBSD.org cc: Eric Anderson Subject: Re: Very low disk performance on 5.x X-BeenThere: freebsd-performance@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Performance/tuning List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 09 May 2005 12:14:27 -0000 In message <20050509203849.J20942@delplex.bde.org>, Bruce Evans writes: >> The solution is to re-engineer the way that I/O buffers pass through >> the kernel and only assign KVA when needed (for doing software parity >> calculations, for example). > >How would it yield anything except complexity and negative performance >benefits on machines that don't need it? The crucial point here is that disk controllers do not need it. Most disk-controller hardware is able to do scatter/gather these days and we cannot exploit that because we insist on disk-I/O happening from sequential KVM addresses. The silly thing about us insisting on KVM mapping in the first place is that there is practically no modern hardware that needs that. ATA in PIO mode. RAID5 parity calculation. GBDE encryption and that is about it. Of course we need to cater for those in the new world order too, but it seems only fair to put the overhead in front of those three since they are already slow operations. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.