From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:32960) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dKfMv-0008Rj-3Z for qemu-devel@nongnu.org; Tue, 13 Jun 2017 02:32:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dKfMq-0000L5-5e for qemu-devel@nongnu.org; Tue, 13 Jun 2017 02:32:01 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59110) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dKfMp-0000Kv-W1 for qemu-devel@nongnu.org; Tue, 13 Jun 2017 02:31:56 -0400 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> <593F827A.9000106@intel.com> From: Jason Wang Message-ID: <74c22cd1-391d-d6b2-03f1-b247c2f78ccf@redhat.com> Date: Tue, 13 Jun 2017 14:31:43 +0800 MIME-Version: 1.0 In-Reply-To: <593F827A.9000106@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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: Wei Wang , "Michael S. Tsirkin" Cc: "virtio-dev@lists.oasis-open.org" , "stefanha@gmail.com" , "qemu-devel@nongnu.org" , "jan.scheurich@ericsson.com" , "armbru@redhat.com" , "marcandre.lureau@gmail.com" , "pbonzini@redhat.com" On 2017=E5=B9=B406=E6=9C=8813=E6=97=A5 14:13, Wei Wang wrote: > On 06/13/2017 11:59 AM, Jason Wang wrote: >> >> On 2017=E5=B9=B406=E6=9C=8813=E6=97=A5 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. What if there's backend that supports less than 1023? Or in the future,=20 we increase the limit to e.g 2048? Thanks > > Best, > Wei >