From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33181) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dSLaC-0000lU-5v for qemu-devel@nongnu.org; Tue, 04 Jul 2017 07:01:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dSLa9-0004AD-5M for qemu-devel@nongnu.org; Tue, 04 Jul 2017 07:01:28 -0400 Received: from mga03.intel.com ([134.134.136.65]:43148) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dSLa8-00049A-S3 for qemu-devel@nongnu.org; Tue, 04 Jul 2017 07:01:25 -0400 Message-ID: <595B7617.4060203@intel.com> Date: Tue, 04 Jul 2017 19:03:51 +0800 From: Wei Wang MIME-Version: 1.0 References: <1498617479-5809-1-git-send-email-wei.w.wang@intel.com> <20170703220017-mutt-send-email-mst@kernel.org> In-Reply-To: <20170703220017-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [virtio-dev] Re: [PATCH v4] virtio-net: enable configurable tx queue size List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: jasowang@redhat.com, eblake@redhat.com, virtio-dev@lists.oasis-open.org, qemu-devel@nongnu.org, armbru@redhat.com, stefanha@gmail.com, marcandre.lureau@gmail.com, pbonzini@redhat.com On 07/04/2017 03:18 AM, Michael S. Tsirkin wrote: > On Wed, Jun 28, 2017 at 10:37:59AM +0800, Wei Wang wrote: >> This patch enables the virtio-net tx queue size to be configurable >> between 256 (the default queue size) and 1024 by the user when the >> vhost-user backend is used. >> >> Currently, the maximum tx queue size for other backends is 512 due >> to the following limitations: >> - QEMU backend: the QEMU backend implementation in some cases may >> send 1024+1 iovs to writev. >> - Vhost_net backend: there are possibilities that the guest sends >> a vring_desc of memory which crosses a MemoryRegion thereby >> generating more than 1024 iovs after translation from guest-physical >> address in the backend. >> >> Signed-off-by: Wei Wang > I was going to apply this, but run into a host of issues: > > This segfaults: > $ ./x86_64-softmmu/qemu-system-x86_64 -device virtio-net,tx_queue_size=1024 > Segmentation fault (core dumped) > > I tried to tweak this code a bit to avoid the crash, and I run into a further issue: > $ ./x86_64-softmmu/qemu-system-x86_64 -device virtio-net,tx_queue_size=1024 > Bad ram offset aa49002 > Aborted (core dumped) > > the second issue is especially concerning. > AFAIK, all the virtio-net backends require "-netdev". I'm wondering if there is any case that virtio-net can work without a "-netdev" created in QEMU? If not, would it be better if we just stop the device creation at the beginning of virtio_net_device_realize() if "-netdev" is not given (i.e. !n->nic_conf.peers.ncs[0])? Best, Wei