From owner-freebsd-multimedia@FreeBSD.ORG Fri Apr 15 07:53:57 2005 Return-Path: Delivered-To: freebsd-multimedia@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id D11B416A4CE for ; Fri, 15 Apr 2005 07:53:57 +0000 (GMT) Received: from mailout01.sul.t-online.com (mailout01.sul.t-online.com [194.25.134.80]) by mx1.FreeBSD.org (Postfix) with ESMTP id D3E5E43D5A for ; Fri, 15 Apr 2005 07:53:56 +0000 (GMT) (envelope-from Alexander@Leidinger.net) Received: from fwd24.aul.t-online.de by mailout01.sul.t-online.com with smtp id 1DMLeC-0000VE-01; Fri, 15 Apr 2005 09:53:52 +0200 Received: from Andro-Beta.Leidinger.net (EIVxdGZTZex773PbpnYVCToLEfKPrOCEO5ad9kN51OAducopBRLYck@[217.229.213.163]) by fwd24.sul.t-online.de with esmtp id 1DMLdw-1432KO0; Fri, 15 Apr 2005 09:53:36 +0200 Received: from localhost (localhost [127.0.0.1])j3F7rZn8076500; Fri, 15 Apr 2005 09:53:35 +0200 (CEST) (envelope-from Alexander@Leidinger.net) Received: from 141.113.101.32 ([141.113.101.32]) by netchild.homeip.net (Horde MIME library) with HTTP for ; Fri, 15 Apr 2005 09:53:35 +0200 Message-ID: <20050415095335.46kkjh7q4gkwook0@netchild.homeip.net> X-Priority: 3 (Normal) Date: Fri, 15 Apr 2005 09:53:35 +0200 From: Alexander Leidinger To: Julian Elischer References: <20050410195645.GA2178@cnd.mcgill.ca> <20050414.021552.343134310.kazuhito@ph.noda.tus.ac.jp> <20050413172534.GF2178@cnd.mcgill.ca> <20050414161546.kwroviadwsw8k0w0@netchild.homeip.net> <425ED3F0.70603@elischer.org> In-Reply-To: <425ED3F0.70603@elischer.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format="flowed" Content-Disposition: inline Content-Transfer-Encoding: 7bit User-Agent: Internet Messaging Program (IMP) H3 (4.0.2) / FreeBSD-4.11 X-ID: EIVxdGZTZex773PbpnYVCToLEfKPrOCEO5ad9kN51OAducopBRLYck@t-dialin.net X-TOI-MSGID: 97dde06e-f651-4b78-90b3-c8abbd3fc31c cc: freebsd-multimedia@freebsd.org cc: Mathew Kanner Subject: Re: de-dma uaudio X-BeenThere: freebsd-multimedia@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Multimedia discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 15 Apr 2005 07:53:57 -0000 Julian Elischer wrote: > The low hardware layer already does DMA to move data out of the > hardware to memory. The data gets copied from the user layer to an > intermediate > buffer and from there to the DMA buffers. There is no need to > allocate DMA capable > buffers for the intermediate layer. I understand this as: userland-mem -> kernel-mem -> dma-able-mem -> hardware So there's no zero-copy behavior? userland-mem -> in-kernel-dma-able-mem -> hardware or userland-mem -> if(is_dmaable(userland-mem)) -> hardware else -> in-kernel-dma-able-mem -> hardware While the amount of memory used as a sound buffer isn't that much for todays standards, it's still a memory transfer operation which could be avoided. I don't know how much it would affect the latency (or if it affects it at all), but not doing things which aren't necesssary/beneficial is always a win (in some way) in my experience. Bye, Alexander. -- http://www.Leidinger.net Alexander @ Leidinger.net: PGP ID = B0063FE7 http://www.FreeBSD.org netchild @ FreeBSD.org : PGP ID = 72077137 The problem that we thought was a problem was, indeed, a problem, but not the problem we thought was the problem. -- Mike Smith