From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from TPC-E3-10-016.phaedrus.sandvine.com (lab.sandvine.com [98.159.241.2]) by dpdk.org (Postfix) with ESMTP id B2C435AB8 for ; Fri, 26 Feb 2016 19:58:36 +0100 (CET) Received: by TPC-E3-10-016.phaedrus.sandvine.com (Postfix, from userid 10523) id 0D49F22248; Fri, 26 Feb 2016 13:58:36 -0500 (EST) From: Kyle Larose To: dev@dpdk.org Date: Fri, 26 Feb 2016 13:58:07 -0500 Message-Id: <1456513087-28644-1-git-send-email-klarose@sandvine.com> X-Mailer: git-send-email 1.8.3.1 Subject: [dpdk-dev] [PATCH] virtio: fix rx ring descriptor starvation X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 26 Feb 2016 18:58:36 -0000 Virtio has an mbuf descriptor ring containing mbufs to be used for receiving traffic. When the host queues traffic to be sent to the guest, it consumes these descriptors. If none exist, it discards the packet. The virtio pmd allocates mbufs to the descriptor ring every time it succesfully receives a packet. However, it never does it if it does not receive a valid packet. If the descriptor ring is exhausted, and the mbuf mempool does not have any mbufs free (which can happen for various reasons, such as queueing along the processing pipeline), then the receive call will not allocate any mbufs to the descriptor ring, and when it finishes, the descriptor ring will be empty. The ring being empty means that we will never receive a packet again, which means we will never allocate mbufs to the ring: we are stuck. Ultimately, the problem arises because there is a dependency between receiving packets and making the descriptor ring not be empty, and a dependency between the descriptor ring not being empty, and receicing packets. To fix the problem, this pakes makes virtio always try to allocate mbufs to the descriptor ring, if necessary, when polling for packets. Do this by removing the early exit if no packets were received. Since the packet loop later will do nothing if there are no packets, this is fine. --- drivers/net/virtio/virtio_rxtx.c | 6 ------ 1 file changed, 6 deletions(-) diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c index 41a1366..9d2f7d6 100644 --- a/drivers/net/virtio/virtio_rxtx.c +++ b/drivers/net/virtio/virtio_rxtx.c @@ -571,9 +571,6 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts) if (likely(num > DESC_PER_CACHELINE)) num = num - ((rxvq->vq_used_cons_idx + num) % DESC_PER_CACHELINE); - if (num == 0) - return 0; - num = virtqueue_dequeue_burst_rx(rxvq, rcv_pkts, len, num); PMD_RX_LOG(DEBUG, "used:%d dequeue:%d", nb_used, num); @@ -671,9 +668,6 @@ virtio_recv_mergeable_pkts(void *rx_queue, virtio_rmb(); - if (nb_used == 0) - return 0; - PMD_RX_LOG(DEBUG, "used:%d\n", nb_used); hw = rxvq->hw; -- 1.8.3.1