From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54591) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f1OLH-0003St-Se for qemu-devel@nongnu.org; Wed, 28 Mar 2018 23:35:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f1OLD-0005yR-UT for qemu-devel@nongnu.org; Wed, 28 Mar 2018 23:35:11 -0400 Received: from mga05.intel.com ([192.55.52.43]:3354) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f1OLD-0005y0-Lp for qemu-devel@nongnu.org; Wed, 28 Mar 2018 23:35:07 -0400 Date: Thu, 29 Mar 2018 11:33:29 +0800 From: Tiwei Bie Message-ID: <20180329033329.ucnx34nzimgec7pp@debian> References: <20180319071537.28649-1-tiwei.bie@intel.com> <20180322181952-mutt-send-email-mst@kernel.org> <20180328122407.gc6yba26gijlm5g6@debian> <20180328183159-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180328183159-mutt-send-email-mst@kernel.org> Subject: Re: [Qemu-devel] [virtio-dev] Re: [PATCH v2 0/6] Extend vhost-user to support VFIO based accelerators List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, virtio-dev@lists.oasis-open.org, alex.williamson@redhat.com, jasowang@redhat.com, pbonzini@redhat.com, stefanha@redhat.com, cunming.liang@intel.com, dan.daly@intel.com, jianfeng.tan@intel.com, zhihong.wang@intel.com, xiao.w.wang@intel.com On Wed, Mar 28, 2018 at 06:33:01PM +0300, Michael S. Tsirkin wrote: > On Wed, Mar 28, 2018 at 08:24:07PM +0800, Tiwei Bie wrote: > > > > Update notes > > > > ============ > > > > > > > > IOMMU feature bit check is removed in this version, because: > > > > > > > > The IOMMU feature is negotiable, when an accelerator is used and > > > > it doesn't support virtual IOMMU, its driver just won't provide > > > > this feature bit when vhost library querying its features. And if > > > > it supports the virtual IOMMU, its driver can provide this feature > > > > bit. It's not reasonable to add this limitation in this patch set. > > > > > > Fair enough. Still: > > > Can hardware on intel platforms actually support IOTLB requests? > > > Don't you need to add support for vIOMMU shadowing instead? > > > > > > > For the hardware I have, I guess they can't for now. > > So VFIO in QEMU has support for vIOMMU shadowing. > Can you use that somehow? Yeah, I guess we can use it in some way. Actually supporting vIOMMU is a quite interesting feature. It would provide better security, and for the hardware backend case there would be no performance penalty with static mapping after the backend got all the mappings. I think it could be done as another work. Based on your previous suggestion in this thread, I have split the guest notification offload and host notification offload (I'll send the new version very soon). And I plan to let this patch set just focus on fixing the most critical performance issue - the host notification offload. With this fix, using hardware backend in vhost-user could get a very big performance boost and become much more practicable. So maybe we can focus on fixing this critical performance issue first. How do you think? > > Ability to run dpdk within guest seems important. I think vIOMMU isn't a must to run DPDK in guest. For Linux guest we also have igb_uio and uio_pci_generic to run DPDK, for FreeBSD guest we have nic_uio. They don't need vIOMMU, and they could offer the best performance. Best regards, Tiwei Bie > > -- > MST > > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org >