From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49682) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eFZRj-00025g-CJ for qemu-devel@nongnu.org; Fri, 17 Nov 2017 00:44:12 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eFZRe-0005rW-GY for qemu-devel@nongnu.org; Fri, 17 Nov 2017 00:44:11 -0500 Received: from szxga05-in.huawei.com ([45.249.212.191]:2731) by eggs.gnu.org with esmtps (TLS1.0:RSA_ARCFOUR_SHA1:16) (Exim 4.71) (envelope-from ) id 1eFZRd-0005pR-Mr for qemu-devel@nongnu.org; Fri, 17 Nov 2017 00:44:06 -0500 Message-ID: <5A0E76F3.9060100@huawei.com> Date: Fri, 17 Nov 2017 13:43:15 +0800 From: "Longpeng (Mike)" MIME-Version: 1.0 References: <5A0D27D8.6050506@huawei.com> <2e0ddd76-3903-d715-9a86-73f1286322e7@redhat.com> <33183CC9F5247A488A2544077AF19020DA46E2A6@DGGEMA505-MBS.china.huawei.com> <6aaaca2b-81ef-a1c1-4745-830d008b3770@redhat.com> <5A0D5B1B.3080708@huawei.com> <55f2edb1-1fe3-d03f-7f4f-418a3b15997a@redhat.com> <20171117063024-mutt-send-email-mst@kernel.org> In-Reply-To: <20171117063024-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Jason Wang , "Huangweidong (C)" , "stefanha@redhat.com" , "qemu-devel@nongnu.org" , "Wangjing (King, Euler)" , "Gonglei (Arei)" , "Longpeng(Mike)" , yvugenfi@redhat.com On 2017/11/17 12:32, Michael S. Tsirkin wrote: > On Thu, Nov 16, 2017 at 08:04:34PM +0800, Jason Wang wrote: >> >> >> On 2017年11月16日 17:32, Longpeng (Mike) wrote: >>> Hi Jason, >>> >>> On 2017/11/16 17:13, Jason Wang wrote: >>> >>>> >>>> On 2017年11月16日 17:01, Gonglei (Arei) wrote: >>>>> No, Windows guest + vhost-user/DPDK. >>>>> >>>>> BTW pls see virtio spec in : >>>>> >>>>> "If VIRTIO_NET_F_MQ is negotiated, each of receiveq1. . .receiveqN that will >>>>> be used SHOULD be populated >>>>> with receive buffers." >>>>> >>>>> It is not mandatory that all queues must be initialized. >>>> I think not, since it said we should fill receive buffers for each queue which >>>> means we should initialize all queues. May Michael can clarify on this. >>>> >>> >>> I think this doesn't matter, but QEMU should consider this scenario... >>> >>> For example, if one queues isn't initialized (Windows guest), the vring.avail=0, >>> so vq->desc_phys=0, then vq->desc='a avail HVA'(which is the start addr of pc.ram). >>> >>> vq->desc_size = s = l = virtio_queue_get_desc_size(vdev, idx); >>> vq->desc_phys = a = virtio_queue_get_desc_addr(vdev, idx); >>> vq->desc = vhost_memory_map(dev, a, &l, 0); >>> if (!vq->desc || l != s) { >>> r = -ENOMEM; >>> goto fail_alloc_desc; >>> } >>> ..... >>> r = vhost_virtqueue_set_addr(dev, vq, vhost_vq_index, dev->log_enabled); >>> if (r < 0) { >>> r = -errno; >>> goto fail_alloc; >>> } >>> >>> Then the HVA is send to the vhost-user. >>> >>> I think this is wrong, because the '0' here means guest driver doesn't init this >>> queues, it should not be used to calculate the HVA for this vq. >> >> Yes, workaround is not hard if windows driver won't use the left 3 queues >> any more. But we should have a complete solution. The main problem is when >> vhost need to be started. For legacy device, there's no easy way to detect >> whether or not a specific virtqueue is ready to be used. For modern device, >> we can probably do this through queue_enable (but this is not implemented in >> current code). >> >> Thanks > > What isn't implemented? > > Spec is quite explicit: > > > Client must only process each ring when it is started. > > Client must only pass data between the ring and the > backend, when the ring is enabled. > > and later: > > > Client must start ring upon receiving a kick (that is, detecting that file > descriptor is readable) on the descriptor specified by > VHOST_USER_SET_VRING_KICK, and stop ring upon receiving > VHOST_USER_GET_VRING_BASE. > > > Does someone kick unused rings? What entity does this? > Hi Michael, Maybe you don't get our point, so let me be clear. :) Suppose there is a VM with 4 vcpus and 7 queues (vhost-user backend), the Windows guest will only initialize the first 4 queues, so in QEMU the addresses of the desc/avail/used tables of last 3 queues are all ZERO (initial value). However QEMU will start all 7 queues, please look at the codes below: ''' vhost_net_start for (i = 0; i < total_queues; i++) // start all 7 queues vhost_net_start_one vhost_dev_start vhost_virtqueue_start ''' In vhost_virtqueue_start(), it will use the ZERO to calculate a corresponding HVA for the last 3 queues and then send to the backend ( by vhost_virtqueue_set_addr() ). So our issue here is: the ZERO here means guest doesn't initialize the last 3 queues, so it needn't to calculate the HVA for them and send to then backend. But, there is no issue on Linux guest, because Linux driver will initialize the desc/avail/used tables for all 7 queues (even if it only uses the first 4 queues). Jason has already get our point, now we need to obtain more information about Windows virtio-net driver from Yan. > > > >>> >>>> Thanks >>>> >>>>> Thanks, >>>>> -Gonglei >>>>> >>>> >>>> >>>> >>>> . >>>> >>> > > . > -- Regards, Longpeng(Mike)