Hi Wenzhuo, On Thu, 2 Mar 2017 01:22:25 +0000, "Lu, Wenzhuo" <wenzhuo...@intel.com> wrote: > Hi Oliver, > > > -----Original Message----- > > From: Olivier Matz [mailto:olivier.m...@6wind.com] > > Sent: Thursday, March 2, 2017 1:19 AM > > To: dev@dpdk.org; thomas.monja...@6wind.com; Ananyev, Konstantin; Lu, > > Wenzhuo; Zhang, Helin; Wu, Jingjing; adrien.mazarg...@6wind.com; > > nelio.laranje...@6wind.com > > Cc: Yigit, Ferruh; Richardson, Bruce > > Subject: [PATCH 4/6] net/e1000: implement descriptor status API (em) > > > > Signed-off-by: Olivier Matz <olivier.m...@6wind.com> > > +int > > +eth_em_tx_descriptor_status(struct rte_eth_dev *dev, uint16_t tx_queue_id, > > + uint16_t offset) > > +{ > > + volatile uint8_t *status; > > + struct em_tx_queue *txq; > > + uint32_t desc; > > + > > + txq = dev->data->tx_queues[tx_queue_id]; > > + if (unlikely(offset >= txq->nb_tx_desc)) > > + return -EINVAL; > > + > > + desc = txq->tx_tail + offset; > > + /* go to next desc that has the RS bit */ > > + desc = ((desc + txq->tx_rs_thresh - 1) / txq->tx_rs_thresh) * > > + txq->tx_rs_thresh; > The descriptor may be changed here. So the return value may not be for the > offset one. Why?
Yes, desc index can change. From what I understand, the "descriptor done" (DD) bit is only set on descriptors which are flagged with the "report status" (RS) bit. Here is an example from: http://www.dpdk.org/ml/archives/dev/2016-November/050679.html |----------------------------------------------------------------| | D R R R | | ............xxxxxxxxxxxxxxxxxxxxxxxxx | | <descs sent><- descs not sent yet -> | | ............xxxxxxxxxxxxxxxxxxxxxxxxx | |----------------------------------------------------------------| ^last_desc_cleaned=8 ^next_rs=47 ^next_dd=15 ^tail=45 ^hw_head=20 <---- nb_used ---------> The hardware is currently processing the descriptor 20 'R' means the descriptor has the RS bit 'D' means the descriptor has the DD + RS bits 'x' are packets in txq (not sent) '.' are packet already sent but not freed by sw Regards, Olivier
