[ovs-dev] [PATCH v2 1/2] netdev-dpdk: Use intermediate queue during packet transmission.

Ilya Maximets i.maximets at samsung.com
Wed Jan 18 07:37:13 UTC 2017


Not a complete review. This code is full of races.
See details inline.

Best regards, Ilya Maximets.

On 17.01.2017 18:37, antonio.fischetti at intel.com wrote:
> This patch implements the intermediate Tx queues on 'dpdk' type ports.
> 
> Test results:
>  * In worst case scenario with fewer packets per batch, a significant
>    bottleneck is observed for netdev_dpdk_eth_send() function due to
>    expensive MMIO writes.
> 
>  * Also its observed that CPI(cycles per instruction) Rate for the function
>    stood between 3.15 and 4.1 which is significantly higher than acceptable
>    limit of 1.0 for HPC applications and theoretical limit of 0.25 (As Backend
>    pipeline can retire 4 micro-operations in a cycle).
> 
>  * With this patch, CPI for netdev_dpdk_eth_send() is at 0.55 and the overall
>    throughput improved significantly.
> 
> 
> Signed-off-by: Antonio Fischetti <antonio.fischetti at intel.com>
> Signed-off-by: Bhanuprakash Bodireddy <bhanuprakash.bodireddy at intel.com>
> Co-authored-by: Bhanuprakash Bodireddy <bhanuprakash.bodireddy at intel.com>
> Signed-off-by: Markus Magnusson <markus.magnusson at ericsson.com>
> Co-authored-by: Markus Magnusson <markus.magnusson at ericsson.com>
> ---
>  lib/dpif-netdev.c     | 53 +++++++++++++++++++++++++++++++--
>  lib/netdev-bsd.c      |  1 +
>  lib/netdev-dpdk.c     | 82 ++++++++++++++++++++++++++++++++++++++++++++++-----
>  lib/netdev-dummy.c    |  1 +
>  lib/netdev-linux.c    |  1 +
>  lib/netdev-provider.h |  8 +++++
>  lib/netdev-vport.c    |  3 +-
>  lib/netdev.c          |  9 ++++++
>  lib/netdev.h          |  1 +
>  9 files changed, 149 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index 3901129..58ac429 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -289,6 +289,8 @@ struct dp_netdev_rxq {
>      struct dp_netdev_pmd_thread *pmd;  /* pmd thread that will poll this queue. */
>  };
>  
> +#define LAST_USED_QID_NONE -1
> +
>  /* A port in a netdev-based datapath. */
>  struct dp_netdev_port {
>      odp_port_t port_no;
> @@ -303,6 +305,8 @@ struct dp_netdev_port {
>      char *type;                 /* Port type as requested by user. */
>      char *rxq_affinity_list;    /* Requested affinity of rx queues. */
>      bool need_reconfigure;      /* True if we should reconfigure netdev. */
> +    int last_used_qid;          /* Last queue id where packets could be
> +                                   enqueued. */
>  };
>  
>  /* Contained by struct dp_netdev_flow's 'stats' member.  */
> @@ -619,6 +623,9 @@ static int dpif_netdev_xps_get_tx_qid(const struct dp_netdev_pmd_thread *pmd,
>  static inline bool emc_entry_alive(struct emc_entry *ce);
>  static void emc_clear_entry(struct emc_entry *ce);
>  
> +static struct tx_port *pmd_send_port_cache_lookup
> +(const struct dp_netdev_pmd_thread *pmd, odp_port_t port_no);
> +
>  static void
>  emc_cache_init(struct emc_cache *flow_cache)
>  {
> @@ -3507,15 +3514,19 @@ pmd_load_queues_and_ports(struct dp_netdev_pmd_thread *pmd,
>      return i;
>  }
>  
> +enum { DRAIN_TSC = 20000ULL };
> +
>  static void *
>  pmd_thread_main(void *f_)
>  {
>      struct dp_netdev_pmd_thread *pmd = f_;
> -    unsigned int lc = 0;
> +    unsigned int lc = 0, lc_drain = 0;
>      struct polled_queue *poll_list;
>      bool exiting;
>      int poll_cnt;
>      int i;
> +    uint64_t prev = 0, now = 0;
> +    struct tx_port *tx_port;
>  
>      poll_list = NULL;
>  
> @@ -3548,6 +3559,26 @@ reload:
>                                         poll_list[i].port_no);
>          }
>  
> +#define MAX_LOOP_TO_DRAIN 128
> +        if (lc_drain++ > MAX_LOOP_TO_DRAIN) {
> +            lc_drain = 0;
> +            prev = now;
> +            now = pmd->last_cycles;
> +            if ((now - prev) > DRAIN_TSC) {
> +                HMAP_FOR_EACH (tx_port, node, &pmd->tx_ports) {

'pmd->tx_ports' must be protected by 'pmd->port_mutex'. Also it can be changed
while pmd still working. I think you wanted something like 'pmd->send_port_cache'.

> +                    if (tx_port->port->last_used_qid != LAST_USED_QID_NONE) {
> +                        /* This queue may contain some buffered packets waiting
> +                         * to be sent out. */
> +                        netdev_txq_drain(tx_port->port->netdev,
> +                                tx_port->port->last_used_qid,
> +                                tx_port->port->dynamic_txqs);
> +                        /* Mark it as empty. */
> +                        tx_port->port->last_used_qid = LAST_USED_QID_NONE;

'port' is a pointer to the common structure --> 'port->last_used_qid' will be
concurrently updated by all threads --> total mess.

> +                    }
> +                }
> +            }
> +        }
> +
>          if (lc++ > 1024) {
>              bool reload;
>  
> @@ -3883,6 +3914,7 @@ dp_netdev_add_port_tx_to_pmd(struct dp_netdev_pmd_thread *pmd,
>  
>      tx->port = port;
>      tx->qid = -1;
> +    port->last_used_qid = LAST_USED_QID_NONE;
>  
>      hmap_insert(&pmd->tx_ports, &tx->node, hash_port_no(tx->port->port_no));
>      pmd->need_reload = true;
> @@ -4538,7 +4570,24 @@ dp_execute_cb(void *aux_, struct dp_packet_batch *packets_,
>              } else {
>                  tx_qid = pmd->static_tx_qid;
>              }
> +//TODO Add UNLIKELY to the 1st condition?
> +            /* Is the current qid the same as the last one we used? */
> +            if ((p->port->last_used_qid != LAST_USED_QID_NONE) &&
> +                (p->port->last_used_qid != tx_qid)) {
> +                /* The current assigned queue was changed, we need to drain
> +                 * packets from the previous queue. */
> +                netdev_txq_drain(p->port->netdev,
> +                        p->port->last_used_qid,
> +                        p->port->dynamic_txqs);
> +                p->port->last_used_qid = LAST_USED_QID_NONE;
> +            }
>  
> +            /* In case these packets gets buffered into an intermediate
> +             * queue and XPS is enabled the drain function could find a
> +             * different Tx qid assigned to its thread.  We keep track
> +             * of the qid we're now using, that will trigger the drain
> +             * function and will select the right queue to flush. */
> +            p->port->last_used_qid = tx_qid;
>              netdev_send(p->port->netdev, tx_qid, packets_, may_steal,
>                          dynamic_txqs);
>              return;
> @@ -4952,7 +5001,7 @@ dpif_dummy_register(enum dummy_level level)
>                               "dp port new-number",
>                               3, 3, dpif_dummy_change_port_number, NULL);
>  }
> -
> +
>  /* Datapath Classifier. */
>  
>  /* A set of rules that all have the same fields wildcarded. */
> diff --git a/lib/netdev-bsd.c b/lib/netdev-bsd.c
> index 94c515d..00d5263 100644
> --- a/lib/netdev-bsd.c
> +++ b/lib/netdev-bsd.c
> @@ -1547,6 +1547,7 @@ netdev_bsd_update_flags(struct netdev *netdev_, enum netdev_flags off,
>      netdev_bsd_rxq_recv,                             \
>      netdev_bsd_rxq_wait,                             \
>      netdev_bsd_rxq_drain,                            \
> +    NULL,                                            \
>  }
>  
>  const struct netdev_class netdev_bsd_class =
> diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
> index 94568a1..d560bf6 100644
> --- a/lib/netdev-dpdk.c
> +++ b/lib/netdev-dpdk.c
> @@ -166,7 +166,6 @@ static const struct rte_eth_conf port_conf = {
>  
>  enum { DPDK_RING_SIZE = 256 };
>  BUILD_ASSERT_DECL(IS_POW2(DPDK_RING_SIZE));
> -enum { DRAIN_TSC = 200000ULL };
>  
>  enum dpdk_dev_type {
>      DPDK_DEV_ETH = 0,
> @@ -289,12 +288,18 @@ struct dpdk_mp {
>  /* There should be one 'struct dpdk_tx_queue' created for
>   * each cpu core. */
>  struct dpdk_tx_queue {
> +    int count;                     /* Number of buffered packets waiting to
> +                                      be sent. */
>      rte_spinlock_t tx_lock;        /* Protects the members and the NIC queue
>                                      * from concurrent access.  It is used only
>                                      * if the queue is shared among different
>                                      * pmd threads (see 'concurrent_txq'). */
>      int map;                       /* Mapping of configured vhost-user queues
>                                      * to enabled by guest. */
> +    struct rte_mbuf *burst_pkts[NETDEV_MAX_BURST];
> +                                   /* Intermediate queues where packets can
> +                                    * be buffered to amortize the cost of MMIO
> +                                    * writes. */
>  };
>  
>  /* dpdk has no way to remove dpdk ring ethernet devices
> @@ -1381,6 +1386,7 @@ static inline int
>  netdev_dpdk_eth_tx_burst(struct netdev_dpdk *dev, int qid,
>                           struct rte_mbuf **pkts, int cnt)
>  {
> +    struct dpdk_tx_queue *txq = &dev->tx_q[qid];
>      uint32_t nb_tx = 0;
>  
>      while (nb_tx != cnt) {
> @@ -1404,6 +1410,8 @@ netdev_dpdk_eth_tx_burst(struct netdev_dpdk *dev, int qid,
>          }
>      }
>  
> +    txq->count = cnt - nb_tx;
> +
>      return cnt - nb_tx;
>  }
>  
> @@ -1788,6 +1796,37 @@ dpdk_do_tx_copy(struct netdev *netdev, int qid, struct dp_packet_batch *batch)
>      }
>  }
>  
> +/* Enqueue packets in an intermediate queue and call the burst
> + * function when the queue is full.  This way we can amortize the
> + * cost of MMIO writes. */
> +static inline int
> +netdev_dpdk_eth_tx_queue(struct netdev_dpdk *dev, int qid,
> +                            struct rte_mbuf **pkts, int cnt)
> +{
> +    struct dpdk_tx_queue *txq = &dev->tx_q[qid];
> +
> +    int i = 0;
> +    int dropped = 0;
> +
> +    while (i < cnt) {
> +        int freeslots = NETDEV_MAX_BURST - txq->count;
> +        int tocopy = MIN(freeslots, cnt-i);
> +
> +        memcpy(&txq->burst_pkts[txq->count], &pkts[i],
> +               tocopy * sizeof (struct rte_mbuf *));
> +
> +        txq->count += tocopy;
> +        i += tocopy;
> +
> +        /* Queue full, burst the packets */
> +        if (txq->count >= NETDEV_MAX_BURST) {
> +           dropped += netdev_dpdk_eth_tx_burst(dev, qid, txq->burst_pkts,
> +                   txq->count);
> +        }
> +    }
> +    return dropped;
> +}
> +
>  static int
>  netdev_dpdk_vhost_send(struct netdev *netdev, int qid,
>                         struct dp_packet_batch *batch,
> @@ -1836,7 +1875,7 @@ netdev_dpdk_send__(struct netdev_dpdk *dev, int qid,
>          cnt = netdev_dpdk_qos_run(dev, pkts, cnt);
>          dropped = batch->count - cnt;
>  
> -        dropped += netdev_dpdk_eth_tx_burst(dev, qid, pkts, cnt);
> +        dropped += netdev_dpdk_eth_tx_queue(dev, qid, pkts, cnt);
>  
>          if (OVS_UNLIKELY(dropped)) {
>              rte_spinlock_lock(&dev->stats_lock);
> @@ -1850,6 +1889,30 @@ netdev_dpdk_send__(struct netdev_dpdk *dev, int qid,
>      }
>  }
>  
> +/* Drain tx queues, this is called periodically to empty the
> + * intermediate queue in case of few packets (< NETDEV_MAX_BURST)
> + * are buffered into the queue. */
> +static int
> +netdev_dpdk_txq_drain(struct netdev *netdev, int qid, bool concurrent_txq)
> +{
> +    struct netdev_dpdk *dev = netdev_dpdk_cast(netdev);
> +    struct dpdk_tx_queue *txq = &dev->tx_q[qid];
> +
> +    if (OVS_LIKELY(txq->count)) {
> +        if (OVS_UNLIKELY(concurrent_txq)) {
> +            qid = qid % dev->up.n_txq;  // TODO: do we need this?
> +            rte_spinlock_lock(&dev->tx_q[qid].tx_lock);
> +        }
> +
> +        netdev_dpdk_eth_tx_burst(dev, qid, txq->burst_pkts, txq->count);
> +
> +        if (OVS_UNLIKELY(concurrent_txq)) {
> +            rte_spinlock_unlock(&dev->tx_q[qid].tx_lock);
> +        }
> +    }
> +    return 0;
> +}
> +
>  static int
>  netdev_dpdk_eth_send(struct netdev *netdev, int qid,
>                       struct dp_packet_batch *batch, bool may_steal,
> @@ -3243,7 +3306,7 @@ unlock:
>                            SET_CONFIG, SET_TX_MULTIQ, SEND,    \
>                            GET_CARRIER, GET_STATS,             \
>                            GET_FEATURES, GET_STATUS,           \
> -                          RECONFIGURE, RXQ_RECV)              \
> +                          RECONFIGURE, RXQ_RECV, TXQ_DRAIN)   \
>  {                                                             \
>      NAME,                                                     \
>      true,                       /* is_pmd */                  \
> @@ -3310,6 +3373,7 @@ unlock:
>      RXQ_RECV,                                                 \
>      NULL,                       /* rx_wait */                 \
>      NULL,                       /* rxq_drain */               \
> +    TXQ_DRAIN,      /* txq_drain */               \
>  }
>  
>  static const struct netdev_class dpdk_class =
> @@ -3326,7 +3390,8 @@ static const struct netdev_class dpdk_class =
>          netdev_dpdk_get_features,
>          netdev_dpdk_get_status,
>          netdev_dpdk_reconfigure,
> -        netdev_dpdk_rxq_recv);
> +        netdev_dpdk_rxq_recv,
> +        netdev_dpdk_txq_drain);
>  
>  static const struct netdev_class dpdk_ring_class =
>      NETDEV_DPDK_CLASS(
> @@ -3342,7 +3407,8 @@ static const struct netdev_class dpdk_ring_class =
>          netdev_dpdk_get_features,
>          netdev_dpdk_get_status,
>          netdev_dpdk_reconfigure,
> -        netdev_dpdk_rxq_recv);
> +        netdev_dpdk_rxq_recv,
> +        NULL);
>  
>  static const struct netdev_class dpdk_vhost_class =
>      NETDEV_DPDK_CLASS(
> @@ -3358,7 +3424,8 @@ static const struct netdev_class dpdk_vhost_class =
>          NULL,
>          NULL,
>          netdev_dpdk_vhost_reconfigure,
> -        netdev_dpdk_vhost_rxq_recv);
> +        netdev_dpdk_vhost_rxq_recv,
> +        NULL);
>  static const struct netdev_class dpdk_vhost_client_class =
>      NETDEV_DPDK_CLASS(
>          "dpdkvhostuserclient",
> @@ -3373,7 +3440,8 @@ static const struct netdev_class dpdk_vhost_client_class =
>          NULL,
>          NULL,
>          netdev_dpdk_vhost_client_reconfigure,
> -        netdev_dpdk_vhost_rxq_recv);
> +        netdev_dpdk_vhost_rxq_recv,
> +        NULL);
>  
>  void
>  netdev_dpdk_register(void)
> diff --git a/lib/netdev-dummy.c b/lib/netdev-dummy.c
> index e6e36cd..6a8ad45 100644
> --- a/lib/netdev-dummy.c
> +++ b/lib/netdev-dummy.c
> @@ -1409,6 +1409,7 @@ netdev_dummy_update_flags(struct netdev *netdev_,
>      netdev_dummy_rxq_recv,                                      \
>      netdev_dummy_rxq_wait,                                      \
>      netdev_dummy_rxq_drain,                                     \
> +    NULL,                                                       \
>  }
>  
>  static const struct netdev_class dummy_class =
> diff --git a/lib/netdev-linux.c b/lib/netdev-linux.c
> index a5a9ec1..2499b3e 100644
> --- a/lib/netdev-linux.c
> +++ b/lib/netdev-linux.c
> @@ -2831,6 +2831,7 @@ netdev_linux_update_flags(struct netdev *netdev_, enum netdev_flags off,
>      netdev_linux_rxq_recv,                                      \
>      netdev_linux_rxq_wait,                                      \
>      netdev_linux_rxq_drain,                                     \
> +    NULL,                                                       \
>  }
>  
>  const struct netdev_class netdev_linux_class =
> diff --git a/lib/netdev-provider.h b/lib/netdev-provider.h
> index 8346fc4..97e72c6 100644
> --- a/lib/netdev-provider.h
> +++ b/lib/netdev-provider.h
> @@ -335,6 +335,11 @@ struct netdev_class {
>       * If the function returns a non-zero value, some of the packets might have
>       * been sent anyway.
>       *
> +     * Some netdev provider - like in case of 'dpdk' - may buffer the batch
> +     * of packets into an intermediate queue.  Buffered packets will be sent
> +     * out when their number will exceed a threshold or by the periodic call
> +     * to the drain function.
> +     *
>       * If 'may_steal' is false, the caller retains ownership of all the
>       * packets.  If 'may_steal' is true, the caller transfers ownership of all
>       * the packets to the network device, regardless of success.
> @@ -769,6 +774,9 @@ struct netdev_class {
>  
>      /* Discards all packets waiting to be received from 'rx'. */
>      int (*rxq_drain)(struct netdev_rxq *rx);
> +
> +    /* Drain all packets waiting to be sent on queue 'qid'. */
> +    int (*txq_drain)(struct netdev *netdev, int qid, bool concurrent_txq);
>  };
>  
>  int netdev_register_provider(const struct netdev_class *);
> diff --git a/lib/netdev-vport.c b/lib/netdev-vport.c
> index 4c2ced5..77225b8 100644
> --- a/lib/netdev-vport.c
> +++ b/lib/netdev-vport.c
> @@ -838,7 +838,8 @@ get_stats(const struct netdev *netdev, struct netdev_stats *stats)
>      NULL,                   /* rx_dealloc */                \
>      NULL,                   /* rx_recv */                   \
>      NULL,                   /* rx_wait */                   \
> -    NULL,                   /* rx_drain */
> +    NULL,                   /* rx_drain */                  \
> +    NULL,                   /* tx_drain */
>  
>  
>  #define TUNNEL_CLASS(NAME, DPIF_PORT, BUILD_HEADER, PUSH_HEADER, POP_HEADER)   \
> diff --git a/lib/netdev.c b/lib/netdev.c
> index 839b1f6..0d48e41 100644
> --- a/lib/netdev.c
> +++ b/lib/netdev.c
> @@ -670,6 +670,15 @@ netdev_rxq_drain(struct netdev_rxq *rx)
>              : 0);
>  }
>  
> +/* Flush packets on the queue 'qid'. */
> +int
> +netdev_txq_drain(struct netdev *netdev, int qid, bool netdev_txq_drain)
> +{
> +    return (netdev->netdev_class->txq_drain
> +            ? netdev->netdev_class->txq_drain(netdev, qid, netdev_txq_drain)
> +            : EOPNOTSUPP);
> +}
> +
>  /* Configures the number of tx queues of 'netdev'. Returns 0 if successful,
>   * otherwise a positive errno value.
>   *
> diff --git a/lib/netdev.h b/lib/netdev.h
> index bef9cdd..49969a1 100644
> --- a/lib/netdev.h
> +++ b/lib/netdev.h
> @@ -153,6 +153,7 @@ int netdev_rxq_drain(struct netdev_rxq *);
>  int netdev_send(struct netdev *, int qid, struct dp_packet_batch *,
>                  bool may_steal, bool concurrent_txq);
>  void netdev_send_wait(struct netdev *, int qid);
> +int netdev_txq_drain(struct netdev *, int qid, bool concurrent_txq);
>  
>  /* native tunnel APIs */
>  /* Structure to pass parameters required to build a tunnel header. */
> 


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