From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57530) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dKf2d-0002Nz-Me for qemu-devel@nongnu.org; Tue, 13 Jun 2017 02:11:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dKf2a-0003if-CZ for qemu-devel@nongnu.org; Tue, 13 Jun 2017 02:11:03 -0400 Received: from mga03.intel.com ([134.134.136.65]:45953) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dKf2a-0003iV-3Y for qemu-devel@nongnu.org; Tue, 13 Jun 2017 02:11:00 -0400 Message-ID: <593F827A.9000106@intel.com> Date: Tue, 13 Jun 2017 14:13:14 +0800 From: Wei Wang MIME-Version: 1.0 References: <1496653049-44530-1-git-send-email-wei.w.wang@intel.com> <20170605182514-mutt-send-email-mst@kernel.org> <5937511D.5070205@intel.com> <20170608220006-mutt-send-email-mst@kernel.org> <593A0F47.5080806@intel.com> <593E5F46.5080704@intel.com> <20170612234035-mutt-send-email-mst@kernel.org> <593F57C0.9080701@intel.com> <4639c51b-32a6-3528-2ed6-c5f6296b6300@redhat.com> <593F6133.9050804@intel.com> <65faf3f9-a839-0b04-c740-6b2a60a51cf6@redhat.com> In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [virtio-dev] Re: [PATCH v1] virtio-net: enable configurable tx queue size List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jason Wang , "Michael S. Tsirkin" Cc: "virtio-dev@lists.oasis-open.org" , "stefanha@gmail.com" , "armbru@redhat.com" , "jan.scheurich@ericsson.com" , "qemu-devel@nongnu.org" , "marcandre.lureau@gmail.com" , "pbonzini@redhat.com" On 06/13/2017 11:59 AM, Jason Wang wrote: > > On 2017年06月13日 11:55, Jason Wang wrote: >> The issue is what if there's a mismatch of max #sgs between qemu and >> vhost? >> >>> When the vhost backend is used, QEMU is not involved in the data >>> path. The vhost backend >>> directly gets what is offered by the guest from the vq. > FYI, qemu will try to fallback to userspace if there's something wrong > with vhost-kernel (e.g the IOMMU support). This doesn't work for > vhost-user actually, but it works for vhost-kernel. > > Thanks > That wouldn't be a problem. When it falls back to the QEMU backend, the "max_chain_size" will be set according to the QEMU backend (e.g. 1023). Guest will read the max_chain_size register. Best, Wei