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Date: Thu, 26 Mar 2015 20:31:05 +0530
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From: Srinivasreddy R <srinivasreddy4390@gmail.com>
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Subject: [dpdk-dev] usvhost interface dropping packets
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hi,
I am using usvhost interfaces for VM to VM communication with ovdk Version
1.2 .
when i am sending packets form one VM to another using PacketGen , i
observed packet drop .
the reason for this is , when packets are send in burst on vhost interface
it checks for the free entries in vhost_virtqueue .if the free enteries are
not available it  retries and waits for some time . then the ovdk drops the
packets .


my question is :
How can i avoid packet drop .
i tried increasing retries and delay . it helped in reducing the loss but
not completely .
is there any solution for avoiding the drop . i have observed drop even at
a very less traffic .
am i missing any thing .
how can i proceed further .


the code part is :
FILE : *rte_port_vhost.c*

static inline uint32_t __attribute__((always_inline))
pf_vhost_enqueue_burst(struct virtio_net *dev, struct rte_mbuf **pkts,
unsigned count)
{
    struct vhost_virtqueue *vq;
    struct vring_desc *desc;

    MODULE_DBG_LOG( "(%"PRIu64") virtio_dev_rx()\n", dev->device_fh);

    vq = dev->virtqueue[VIRTIO_RXQ];
    count = (count > PKT_BURST_SIZE) ? PKT_BURST_SIZE : count;

    /* As many data cores may want access to available buffers, they need
to be reserved. */
    do {
        res_base_idx = vq->last_used_idx_res;
        avail_idx = *((volatile uint16_t *)&vq->avail->idx);

        free_entries = (avail_idx - res_base_idx);
        /* If retry is enabled and the queue is full then we wait and retry
to avoid packet loss. */
        if (unlikely(count > free_entries)) {
            for (retry = 0; retry < g_burst_tx_retry_num; retry++) {
                rte_delay_us(g_burst_tx_delay_time);
                avail_idx =
                    *((volatile uint16_t *)&vq->avail->idx);
                free_entries = (avail_idx - res_base_idx);
                if (count <= free_entries)
                    break;
            }
        }




----------
thanks
srinivas.