Add a statistic to help diagnose contention on the vhost txqs. This is usually seen as dropped packets on the physical ports for rates that are usually handled fine by OVS.
Signed-off-by: David Marchand <[email protected]> --- This patch applies on top of Kevin "vhost-retry" series [1]. 1: https://patchwork.ozlabs.org/project/openvswitch/list/?submitter=70482 --- Documentation/topics/dpdk/vhost-user.rst | 25 +++++++++++++++++++++++++ lib/netdev-dpdk.c | 20 ++++++++++++++++++-- 2 files changed, 43 insertions(+), 2 deletions(-) diff --git a/Documentation/topics/dpdk/vhost-user.rst b/Documentation/topics/dpdk/vhost-user.rst index 724aa62..e276b21 100644 --- a/Documentation/topics/dpdk/vhost-user.rst +++ b/Documentation/topics/dpdk/vhost-user.rst @@ -553,6 +553,31 @@ shown with:: $ ovs-vsctl get Interface dpdkvhostclient0 statistics:tx_retries +vhost tx contention +------------------- + +Contrary to physical ports where the number of Transmit queues is decided at +the configuration of the port and does not change once set up, the number of +Transmit queues for a vhost-user or vhost-user-client interface is negociated +with the guest when its driver enables a virtio interface and OVS has no +control over it. + +Each PMD threads needs a Transmit queue to send packet on such a port. +To accomodate with the cases where the number of PMD threads differs from the +number of Transmit queues enabled by a Virtual Machine, the Transmit queues are +distributed among the PMD threads and their accesses are protected by a +spinlock. + +When contention occurs (because two PMD threads are mapped to the same Transmit +queue), it can be hard to understand this phenomenon. +It usually will be seen as OVS taking more cycles to handle the packet and can +be seen as packets getting dropped on the receive side (rx_dropped statistic +on the physical ports). + +A statistic for the port is available to catch those cases:: + + ovs-vsctl get Interface dpdkvhostclient0 statistics:tx_contentions + vhost-user Dequeue Zero Copy (experimental) ------------------------------------------- diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c index 0e70e44..844fb3c 100644 --- a/lib/netdev-dpdk.c +++ b/lib/netdev-dpdk.c @@ -139,10 +139,11 @@ BUILD_ASSERT_DECL((MAX_NB_MBUF / ROUND_DOWN_POW2(MAX_NB_MBUF / MIN_NB_MBUF)) #define XSTAT_RX_JABBER_ERRORS "rx_jabber_errors" /* Size of vHost custom stats. */ -#define VHOST_CUSTOM_STATS_SIZE 1 +#define VHOST_CUSTOM_STATS_SIZE 2 /* Names of vHost custom stats. */ #define VHOST_STAT_TX_RETRIES "tx_retries" +#define VHOST_STAT_TX_CONTENTIONS "tx_contentions" #define SOCKET0 0 @@ -340,6 +341,8 @@ struct dpdk_tx_queue { * pmd threads (see 'concurrent_txq'). */ int map; /* Mapping of configured vhost-user queues * to enabled by guest. */ + uint64_t tx_contentions; /* Number of times a pmd has been waiting + * for another to xmit on this queue. */ }; /* dpdk has no way to remove dpdk ring ethernet devices @@ -2387,7 +2390,10 @@ __netdev_dpdk_vhost_send(struct netdev *netdev, int qid, goto out; } - rte_spinlock_lock(&dev->tx_q[qid].tx_lock); + if (unlikely(!rte_spinlock_trylock(&dev->tx_q[qid].tx_lock))) { + rte_spinlock_lock(&dev->tx_q[qid].tx_lock); + atomic_count_inc64(&dev->tx_q[qid].tx_contentions); + } cnt = netdev_dpdk_filter_packet_len(dev, cur_pkts, cnt); /* Check has QoS has been configured for the netdev */ @@ -2878,6 +2884,16 @@ netdev_dpdk_vhost_get_custom_stats(const struct netdev *netdev, custom_stats->counters[0].value = dev->tx_retries; rte_spinlock_unlock(&dev->stats_lock); + ovs_strlcpy(custom_stats->counters[1].name, VHOST_STAT_TX_CONTENTIONS, + NETDEV_CUSTOM_STATS_NAME_SIZE); + custom_stats->counters[1].value = 0; + for (unsigned int i = 0; i < netdev->n_txq; i++) { + uint64_t tx_contentions; + + atomic_read_relaxed(&dev->tx_q[i].tx_contentions, &tx_contentions); + custom_stats->counters[1].value += tx_contentions; + } + ovs_mutex_unlock(&dev->mutex); return 0; -- 1.8.3.1 _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
