From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51792) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cjBpP-0003rU-1r for qemu-devel@nongnu.org; Wed, 01 Mar 2017 16:30:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cjBpL-0005gZ-TI for qemu-devel@nongnu.org; Wed, 01 Mar 2017 16:30:31 -0500 Received: from mga03.intel.com ([134.134.136.65]:34604) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cjBpL-0005fd-JZ for qemu-devel@nongnu.org; Wed, 01 Mar 2017 16:30:27 -0500 Date: Wed, 1 Mar 2017 13:30:23 -0800 From: "Raj, Ashok" Message-ID: <20170301213023.fv5utdpbh4zvsxdy@araj-mobl1> References: <20170228220719.GD2352@char.us.ORACLE.com> <20170301210938.GE9043@char.us.ORACLE.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170301210938.GE9043@char.us.ORACLE.com> Subject: Re: [Qemu-devel] [RFC Design Doc v3] Enable Shared Virtual Memory feature in pass-through scenarios List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Konrad Rzeszutek Wilk Cc: "Tian, Kevin" , "Lan, Tianyu" , "Peng, Chao P" , "kvm@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "Hao, Xudong" , "qemu-devel@nongnu.org" , "Sun, Yi Y" , "Pan, Jacob jun" , Ashok Raj On Wed, Mar 01, 2017 at 04:09:38PM -0500, Konrad Rzeszutek Wilk wrote: > .snip.. > > > > No. SVM is purely about sharing CPU address space with device. Command > > submission is still through kernel driver which controls rings (with SVM then > > you can put VA into those commands). There are other vendor specific > > features to enable direct user space submission which is orthogonal to SVM. > > Apologies for my ignorance but how is this beneficial? As in > currently you would put in bus addresses on the ring, but now you > can put VA addresses. > > The obvious benefit I see is that you omit the DMA ops which means there is > less of 'lookup' (VA->bus address) in software - but I would have thought this > would be negligible performance impact? And now the IOMMU alongside with > the CPU would do this lookup. > > Or are there some other improvements in this? Other benefits include, - Application can simply pass its pointers to the SVM capable devices. which means no memory registration overhead to get IO Virtual Addresses. - No need to pin memory for DMA, since the devices can handle faults and can request pages to be paged-in on demand. > > > > > Thanks > > Kevin > _______________________________________________ > iommu mailing list > iommu@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/iommu