Hi Honnappa, > -----Original Message----- > From: Honnappa Nagarahalli <[email protected]> > Sent: Wednesday, February 9, 2022 12:36 PM > To: Xing, Beilei <[email protected]>; [email protected] > Cc: Feifei Wang <[email protected]>; Ruifeng Wang > <[email protected]>; Yigit, Ferruh <[email protected]>; Richardson, > Bruce <[email protected]>; nd <[email protected]>; nd <[email protected]> > Subject: Questions on i40e TX path > > Hi Beilei, > I want to make sure my understanding of the TX path is correct. > Following is my understanding. > > 1) The RS bit must be set in the TX descriptors to ask the NIC to report back > the > send status. Not for each Tx descriptor. According to the datasheet, " The RS flag can be set only on a last Transmit Data Descriptor of a packet or last Transmit Data Descriptor of a TSO or last Transmit Data Descriptor of a filter."
> 2) The NIC reports the send completion by setting the DTYPE field to 0xf. This > also indicates that all the earlier descriptors are also done sending the > packets. Yes. > 3) The check "if (txq->nb_tx_free < txq->tx_free_thresh)" is mainly to ensure > that > we do not check the "descriptor done" status too often. This condition is to ensure there're enough free descriptors for Tx, avoid Tx ring full. > > Is my understanding correct? > > Thank you, > Honnappa
