[dpdk-dev] condition for calling ixgbe_xmit_cleanup

Qing Wan qwan at evertz.com
Wed Feb 12 23:50:03 CET 2014



There are following code in function ixgbe_xmit_pkts,


if ((txq->nb_tx_desc - txq->nb_tx_free) > txq->tx_free_thresh) {




My understanding is, nb_tx_desc means total number of descriptors in
ring and nx_tx_free represents how many descriptors are available, so
txq->nb_tx_desc - txq->nb_tx_free means how many we have used. I'm not
quite understand the meaning of this comparison.  Why is the condition
not something like "if (txq->nb_tx_free < tx_free_thresh)". 


really appreciate if someone could help me on this.




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