[dpdk-dev] [PATCH 4/6] net/e1000: implement descriptor status API (em)

Lu, Wenzhuo wenzhuo.lu at intel.com
Fri Mar 3 02:15:45 CET 2017


Hi Olivier,

> -----Original Message-----
> From: Olivier Matz [mailto:olivier.matz at 6wind.com]
> Sent: Thursday, March 2, 2017 10:47 PM
> To: Lu, Wenzhuo
> Cc: dev at dpdk.org; thomas.monjalon at 6wind.com; Ananyev, Konstantin; Zhang,
> Helin; Wu, Jingjing; adrien.mazarguil at 6wind.com; nelio.laranjeiro at 6wind.com;
> Yigit, Ferruh; Richardson, Bruce
> Subject: Re: [PATCH 4/6] net/e1000: implement descriptor status API (em)
> 
> Hi Wenzhuo,
> 
> On Thu, 2 Mar 2017 01:22:25 +0000, "Lu, Wenzhuo" <wenzhuo.lu at intel.com>
> wrote:
> > Hi Oliver,
> >
> > > -----Original Message-----
> > > From: Olivier Matz [mailto:olivier.matz at 6wind.com]
> > > Sent: Thursday, March 2, 2017 1:19 AM
> > > To: dev at dpdk.org; thomas.monjalon at 6wind.com; Ananyev, Konstantin;
> > > Lu, Wenzhuo; Zhang, Helin; Wu, Jingjing; adrien.mazarguil at 6wind.com;
> > > nelio.laranjeiro at 6wind.com
> > > Cc: Yigit, Ferruh; Richardson, Bruce
> > > Subject: [PATCH 4/6] net/e1000: implement descriptor status API (em)
> > >
> > > Signed-off-by: Olivier Matz <olivier.matz at 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.
Yes, you're right. Sorry for the noise :)

> 
> 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



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