From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Jg2nX-0004yt-Q9 for qemu-devel@nongnu.org; Sun, 30 Mar 2008 15:02:31 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1Jg2nV-0004yh-Vd for qemu-devel@nongnu.org; Sun, 30 Mar 2008 15:02:31 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Jg2nV-0004ye-Rm for qemu-devel@nongnu.org; Sun, 30 Mar 2008 15:02:29 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1Jg2nV-0004W9-AP for qemu-devel@nongnu.org; Sun, 30 Mar 2008 15:02:29 -0400 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e36.co.us.ibm.com (8.13.8/8.13.8) with ESMTP id m2UJ2RAI030371 for ; Sun, 30 Mar 2008 15:02:27 -0400 Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v8.7) with ESMTP id m2UJ2RIq052414 for ; Sun, 30 Mar 2008 13:02:27 -0600 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m2UJ2QaH024399 for ; Sun, 30 Mar 2008 13:02:27 -0600 Message-ID: <47EFE3C1.1000205@us.ibm.com> Date: Sun, 30 Mar 2008 14:02:25 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 2/6] PCI DMA API References: <1206827760-4566-1-git-send-email-aliguori@us.ibm.com> <200803301118.15663.paul@codesourcery.com> <47EFA6E1.7020401@us.ibm.com> <200803301919.54780.paul@codesourcery.com> In-Reply-To: <200803301919.54780.paul@codesourcery.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paul Brook Cc: kvm-devel@lists.sourceforge.net, Marcelo Tosatti , qemu-devel@nongnu.org, Aurelien Jarno Paul Brook wrote: > On Sunday 30 March 2008, Anthony Liguori wrote: > > The entity processing the data shouldn't need to know or care how the > translation is done. PhysIOVector should describe everything it need to know. > Okay, I'll update. >> What could work is if the DMA API functions mapped PhysIOVector => >> PhysIOVector and then the network and block subsystems could operate on >> a PhysIOVector. I have patches that implement vector IO for net and >> block but didn't want to include them in this series to keep things simple. >> > > IMHO this is the only sane way to implement zero-copy. > > >>>> This enables zero-copy IO to be preformed without introducing >>>> assumptions of phys_ram_base. This API is at the PCI device level to >>>> enable support of per-device IOMMU remapping. >>>> >>> By my reading it *requires* bridges be zero-copy. For big-endian targets >>> we need to ability to byteswap accesses. >>> >> You mean via ld/st_phys? >> > > By whatever means the bridge deems necessary. The whole point of the DMA API > is that you're transferring a block of data. The API allows intermediate > busses to transform that data (and address) without the block handler needing > to know or care. > > With your current scheme a byteswapping bus has to allocate a single large > buffer for the whole vector, even if the device then ends up copying unto a > local buffer in small chunks. > Oh, I see now. The DMA API should have not just a mechanism to do bulk transfers but also provide an interface to do load/store's that could potentially be byte-swapped. I didn't realize buses did that. Regards, Anthony Liguori > Paul >