kni: optimize Rx burst size computation

No reason to check out many entries are in kni->rx_q prior to
actually pulling them from the fifo. You can't dequeue more than
are there anyway. Max entries to dequeue is either the max batch
size or however much space is available on kni->free_q (lesser of the two).

Signed-off-by: Jay Rolette <rolette@infiniteio.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Helin Zhang <helin.zhang@intel.com>

diff --git a/lib/librte_eal/linuxapp/kni/kni_net.c b/lib/librte_eal/linuxapp/kni/kni_net.c
index 9f9022b..b714dea 100644 (file)
--- a/lib/librte_eal/linuxapp/kni/kni_net.c
+++ b/lib/librte_eal/linuxapp/kni/kni_net.c
@@ -131,7 +131,7 @@ kni_net_rx_normal(struct kni_dev *kni)
 {
        unsigned ret;
        uint32_t len;
-       unsigned i, num, num_rq, num_fq;
+       unsigned i, num, num_fq;
        struct rte_kni_mbuf *kva;
        struct rte_kni_mbuf *va[MBUF_BURST_SZ];
        void * data_kva;
@@ -139,24 +139,19 @@ kni_net_rx_normal(struct kni_dev *kni)
        struct sk_buff *skb;
        struct net_device *dev = kni->net_dev;
 
-       /* Get the number of entries in rx_q */
-       num_rq = kni_fifo_count(kni->rx_q);
-
        /* Get the number of free entries in free_q */
-       num_fq = kni_fifo_free_count(kni->free_q);
-
-       /* Calculate the number of entries to dequeue in rx_q */
-       num = min(num_rq, num_fq);
-       num = min(num, (unsigned)MBUF_BURST_SZ);
-
-       /* Return if no entry in rx_q and no free entry in free_q */
-       if (num == 0)
+       if ((num_fq = kni_fifo_free_count(kni->free_q)) == 0) {
+               /* No room on the free_q, bail out */
                return;
+       }
+
+       /* Calculate the number of entries to dequeue from rx_q */
+       num = min(num_fq, (unsigned)MBUF_BURST_SZ);
 
        /* Burst dequeue from rx_q */
        ret = kni_fifo_get(kni->rx_q, (void **)va, num);
        if (ret == 0)
-               return; /* Failing should not happen */
+               return;
 
        /* Transfer received packets to netif */
        for (i = 0; i < num; i++) {