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Tsirkin" To: Jason Wang Cc: Xuan Zhuo , qemu-devel@nongnu.org, Alexander Bulekov Subject: Re: [PATCH v1 2/2] virtio-net: virtio_net_flush_tx() check for per-queue reset Message-ID: <20230130004440-mutt-send-email-mst@kernel.org> References: <20230129025150.119972-1-xuanzhuo@linux.alibaba.com> <20230129025150.119972-3-xuanzhuo@linux.alibaba.com> <1674978207.8889825-4-xuanzhuo@linux.alibaba.com> <1675049912.7650461-1-xuanzhuo@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Jan 30, 2023 at 11:53:18AM +0800, Jason Wang wrote: > On Mon, Jan 30, 2023 at 11:42 AM Xuan Zhuo wrote: > > > > On Mon, 30 Jan 2023 11:01:40 +0800, Jason Wang wrote: > > > On Sun, Jan 29, 2023 at 3:44 PM Xuan Zhuo wrote: > > > > > > > > On Sun, 29 Jan 2023 14:23:21 +0800, Jason Wang wrote: > > > > > On Sun, Jan 29, 2023 at 10:52 AM Xuan Zhuo wrote: > > > > > > > > > > > > Check whether it is per-queue reset state in virtio_net_flush_tx(). > > > > > > > > > > > > Before per-queue reset, we need to recover async tx resources. At this > > > > > > time, virtio_net_flush_tx() is called, but we should not try to send > > > > > > new packets, so virtio_net_flush_tx() should check the current > > > > > > per-queue reset state. > > > > > > > > > > > > Fixes: 7dc6be52 ("virtio-net: support queue reset") > > > > > > Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1451 > > > > > > Reported-by: Alexander Bulekov > > > > > > Signed-off-by: Xuan Zhuo > > > > > > --- > > > > > > hw/net/virtio-net.c | 3 ++- > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > > > > > index 3ae909041a..fba6451a50 100644 > > > > > > --- a/hw/net/virtio-net.c > > > > > > +++ b/hw/net/virtio-net.c > > > > > > @@ -2627,7 +2627,8 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) > > > > > > VirtQueueElement *elem; > > > > > > int32_t num_packets = 0; > > > > > > int queue_index = vq2q(virtio_get_queue_index(q->tx_vq)); > > > > > > - if (!(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) { > > > > > > + if (!(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) || > > > > > > + virtio_queue_reset_state(q->tx_vq)) { > > > > > > > > > > We have other places that check DRIVER_OK do we need to check queue > > > > > reset as well? > > > > > > > > I checked it again. I still think that the location of other checking DRIVER_OK > > > > does not need to check the queue reset. > > > > > > For example, if we don't disable can_receive() when the queue is > > > reset, it means rx may go for virtio_net_receive_rcu(). It means the > > > Qemu is still trying to process the traffic from the network backend > > > like tap which may waste cpu cycles. > > > > > > I think the correct way is to return false when the queue is reset in > > > can_receive(), then the backend poll will be disabled (e.g TAP). When > > > the queue is enabled again, qemu_flush_queued_packets() will wake up > > > the backend polling. > > > > > > Having had time to check other places but it would be better to > > > mention why it doesn't need a check in the changelog. > > > > > > static bool virtio_net_can_receive(NetClientState *nc) > > { > > VirtIONet *n = qemu_get_nic_opaque(nc); > > VirtIODevice *vdev = VIRTIO_DEVICE(n); > > VirtIONetQueue *q = virtio_net_get_subqueue(nc); > > > > if (!vdev->vm_running) { > > return false; > > } > > > > if (nc->queue_index >= n->curr_queue_pairs) { > > return false; > > } > > > > if (!virtio_queue_ready(q->rx_vq) || > > !(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) { > > return false; > > } > > > > return true; > > } > > > > int virtio_queue_ready(VirtQueue *vq) > > { > > return vq->vring.avail != 0; > > } > > > > > > static void __virtio_queue_reset(VirtIODevice *vdev, uint32_t i) > > { > > vdev->vq[i].vring.desc = 0; > > vdev->vq[i].vring.avail = 0; > > vdev->vq[i].vring.used = 0; > > vdev->vq[i].last_avail_idx = 0; > > vdev->vq[i].shadow_avail_idx = 0; > > vdev->vq[i].used_idx = 0; > > vdev->vq[i].last_avail_wrap_counter = true; > > vdev->vq[i].shadow_avail_wrap_counter = true; > > vdev->vq[i].used_wrap_counter = true; > > virtio_queue_set_vector(vdev, i, VIRTIO_NO_VECTOR); > > vdev->vq[i].signalled_used = 0; > > vdev->vq[i].signalled_used_valid = false; > > vdev->vq[i].notification = true; > > vdev->vq[i].vring.num = vdev->vq[i].vring.num_default; > > vdev->vq[i].inuse = 0; > > virtio_virtqueue_reset_region_cache(&vdev->vq[i]); > > } > > > > In the implementation of Per-Queue Reset, for RX, we stop RX by setting vdev->vq[i].vring.avail to 0. > > Ok, but this is kind of fragile (especially when vIOMMU is enabled). > I'd add an explicit check for reset there. It's not great in that spec says avail 0 is actually legal. But I don't really want to see more and more checks. If we are doing cleanups, the right way is probably a new "live" flag that transports can set correctly from the combination of DRIVER_OK, desc, kick, queue_enable, queue_reset and so on. > (probably on top). > > Thanks > > > Then callback can_receive will return False. > > > > > > Thanks. > > > > > > > > > > Thanks > > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > > E.g: > > > > > virtio_net_can_receive() > > > > > virtio_net_tx_{timer|bh}() > > > > > > > > > > Thanks > > > > > > > > > > > return num_packets; > > > > > > } > > > > > > > > > > > > -- > > > > > > 2.32.0.3.g01195cf9f > > > > > > > > > > > > > > > > > > > >