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From: | Jason Wang |
Subject: | Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start |
Date: | Fri, 17 Nov 2017 14:44:57 +0800 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 |
On 2017年11月17日 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). ThanksWhat isn't implemented?
I mean queue_enable. Virtio spec said: queue_enable The driver uses this to selectively prevent the device fromexecuting requests from this virtqueue. 1 - enabled; 0 - disabled.
But we have: case VIRTIO_PCI_COMMON_Q_ENABLE: virtio_queue_set_num(vdev, vdev->queue_sel, proxy->vqs[vdev->queue_sel].num); virtio_queue_set_rings(vdev, vdev->queue_sel, ((uint64_t)proxy->vqs[vdev->queue_sel].desc[1]) << 32 | proxy->vqs[vdev->queue_sel].desc[0], ((uint64_t)proxy->vqs[vdev->queue_sel].avail[1]) << 32 | proxy->vqs[vdev->queue_sel].avail[0], ((uint64_t)proxy->vqs[vdev->queue_sel].used[1]) << 32 | proxy->vqs[vdev->queue_sel].used[0]); proxy->vqs[vdev->queue_sel].enabled = 1; break; So it looks to me that we need: - Not assume the value is 1 - Start or stop vhost virtqueue depends on value Thanks
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?ThanksThanks, -Gonglei.
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