From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-px0-f199.google.com (mail-px0-f199.google.com [209.85.216.199]) by ozlabs.org (Postfix) with ESMTP id 45605B7BE6 for ; Wed, 4 Nov 2009 01:38:47 +1100 (EST) Received: by pxi37 with SMTP id 37so3858993pxi.15 for ; Tue, 03 Nov 2009 06:38:46 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <4AEFEC64.3070608@neli.hopto.org> References: <389deec70911020740k13b56bc6kdad3bfaa39916f54@mail.gmail.com> <15E6E326-D17B-42D7-AA22-2CA319C2A808@kernel.crashing.org> <389deec70911021635v6e12a976t9e20fb5f12d8987b@mail.gmail.com> <4AEFEC64.3070608@neli.hopto.org> Date: Tue, 3 Nov 2009 22:38:46 +0800 Message-ID: <389deec70911030638g4a90dae7hd5a164e3d2bd178f@mail.gmail.com> Subject: Re: mpc8548 does not make use of DMA when doing memory copy? From: hank peng To: Micha Nelissen Content-Type: text/plain; charset=UTF-8 Cc: linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 2009/11/3 Micha Nelissen : > hank peng wrote: >> >> I remember normal memory copy can also be done (chosen by user) by DMA >> engine on IOP80331(Intel embedded cpu, xscale arch), so why ppc >> platform didn't make use of DMA doing memory copy, I think it can >> increase performance, please correct me if I am wrong! > > AFAIK the DMA engine has only an asynchronous mode (not very smart IMHO). > This means you always have the overhead of context switch + interrupt + > context switch, so the transfer has to be quite large for this to pay off. > but if the amount of data I want to copy is big enough? can we benefit from using DMA in such case? > Micha > -- The simplest is not all best but the best is surely the simplest!