Re: [dpdk-dev] [PATCH] net/ixgbe: fix Tx check descriptor status APIs error

["Zhao1, Wei" <wei.zhao1@intel.com>]

> -----Original Message-----
> From: Zhang, Qi Z
> Sent: Monday, June 25, 2018 3:56 PM
> To: Zhao1, Wei <wei.zhao1@intel.com>; dev@dpdk.org
> Cc: Lu, Wenzhuo <wenzhuo.lu@intel.com>; stable@dpdk.org
> Subject: RE: [PATCH] net/ixgbe: fix Tx check descriptor status APIs error
> 
> 
> 
> > -----Original Message-----
> > From: Zhao1, Wei
> > Sent: Monday, June 25, 2018 3:53 PM
> > To: Zhang, Qi Z <qi.z.zhang@intel.com>; dev@dpdk.org
> > Cc: Lu, Wenzhuo <wenzhuo.lu@intel.com>; stable@dpdk.org
> > Subject: RE: [PATCH] net/ixgbe: fix Tx check descriptor status APIs
> > error
> >
> > Hi, qi
> >
> > > -----Original Message-----
> > > From: Zhang, Qi Z
> > > Sent: Monday, June 25, 2018 3:47 PM
> > > To: Zhao1, Wei <wei.zhao1@intel.com>; dev@dpdk.org
> > > Cc: Lu, Wenzhuo <wenzhuo.lu@intel.com>; stable@dpdk.org
> > > Subject: RE: [PATCH] net/ixgbe: fix Tx check descriptor status APIs
> > > error
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Zhao1, Wei
> > > > Sent: Monday, June 25, 2018 2:49 PM
> > > > To: Zhang, Qi Z <qi.z.zhang@intel.com>; dev@dpdk.org
> > > > Cc: Lu, Wenzhuo <wenzhuo.lu@intel.com>; stable@dpdk.org
> > > > Subject: RE: [PATCH] net/ixgbe: fix Tx check descriptor status
> > > > APIs error
> > > >
> > > > Hi，qi
> > > >
> > > > > -----Original Message-----
> > > > > From: Zhang, Qi Z
> > > > > Sent: Monday, June 25, 2018 10:49 AM
> > > > > To: Zhao1, Wei <wei.zhao1@intel.com>; dev@dpdk.org
> > > > > Cc: Lu, Wenzhuo <wenzhuo.lu@intel.com>; stable@dpdk.org
> > > > > Subject: RE: [PATCH] net/ixgbe: fix Tx check descriptor status
> > > > > APIs error
> > > > >
> > > > >
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Zhao1, Wei
> > > > > > Sent: Monday, June 25, 2018 9:58 AM
> > > > > > To: Zhang, Qi Z <qi.z.zhang@intel.com>; dev@dpdk.org
> > > > > > Cc: Lu, Wenzhuo <wenzhuo.lu@intel.com>; stable@dpdk.org
> > > > > > Subject: RE: [PATCH] net/ixgbe: fix Tx check descriptor status
> > > > > > APIs error
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Zhang, Qi Z
> > > > > > > Sent: Friday, June 22, 2018 9:47 PM
> > > > > > > To: Zhao1, Wei <wei.zhao1@intel.com>; dev@dpdk.org
> > > > > > > Cc: Lu, Wenzhuo <wenzhuo.lu@intel.com>; stable@dpdk.org
> > > > > > > Subject: RE: [PATCH] net/ixgbe: fix Tx check descriptor
> > > > > > > status APIs error
> > > > > > >
> > > > > > > Hi Wei:
> > > > > > >
> > > > > > > > -----Original Message-----
> > > > > > > > From: Zhao1, Wei
> > > > > > > > Sent: Friday, June 22, 2018 4:39 PM
> > > > > > > > To: dev@dpdk.org
> > > > > > > > Cc: Lu, Wenzhuo <wenzhuo.lu@intel.com>; Zhang, Qi Z
> > > > > > > > <qi.z.zhang@intel.com>; stable@dpdk.org; Zhao1, Wei
> > > > > > > > <wei.zhao1@intel.com>
> > > > > > > > Subject: [PATCH] net/ixgbe: fix Tx check descriptor status
> > > > > > > > APIs error
> > > > > > > >
> > > > > > > > This is a issue involve RS bit set rule in ixgbe.
> > > > > > > > Let us take function ixgbe_xmit_pkts_vec () as an example,
> > > > > > > > in this function RS bit will be set for descriptor with
> > > > > > > > index
> > > > > > > > txq->tx_next_rs, and also descriptor free function
> > > > > > > > ixgbe_tx_free_bufs() also check RS bit for descriptor with
> > > > > > > > index
> > > > > > > > txq->tx_next_rs, This is perfect ok. Let us take an
> > > > > > > > txq->example,
> > > > > > > > if app set tx_rs_thresh = 32 and nb_desc = 512, then ixgbe
> > > > > > > > PMD code will init
> > > > > > > > txq->tx_next_rs = 31 in function ixgbe_reset_tx_queue when
> > > > > > > > txq->tx queue
> > > > > > > setup.
> > > > > > > > And also txq->tx_next_rs will be update as 63, 95 and so on.
> > > > > > > > But, in the function ixgbe_dev_tx_descriptor_status(), the
> > > > > > > > RS bit to check is " desc = ((desc
> > > > > > > > + txq->tx_rs_thresh - 1) /
> > > > > > > > txq->tx_rs_thresh) * txq-tx_rs_thresh", which is 32 ,64,
> > > > > > > > txq->96 and so
> > > on.
> > > > > > > > So, they are all wrong! In tx function of
> > > > > > > > ixgbe_xmit_pkts_simple, the RS bit rule is also the same,
> > > > > > > > it also set
> > > > index 31 ,64, 95.
> > > > > > > > we need to correct it.
> > > > > > >
> > > > > > > One question:
> > > > > > > does only the descriptor with RS bit will have DD status, or
> > > > > > > NIC will always update all descriptor's DD status but this
> > > > > > > happens when the next descriptor with RS bit has been sent?
> > > > > > > If it is the first case, I think you fix still have problem,
> > > > > > > because multi-seg mbuf or tso offload will break the 31, 63,
> > > > > > > 95 pattern
> > > > > > > See:
> > > > > > > 						nb_used =
> (uint16_t)(tx_pkt-
> > > > > > > >nb_segs + new_ctx);
> > > > > > >
> > > > > > > 						if (txp != NULL &&
> > > > > > >                                 nb_used + txq->nb_tx_used >=
> > > > > > txq->tx_rs_thresh)
> > > > > > >                         /* set RS on the previous packet in
> > > > > > > the burst
> > > > */
> > > > > > >                         txp->read.cmd_type_len |=
> > > > > > >
> > > > > > rte_cpu_to_le_32(IXGBE_TXD_CMD_RS);
> > > > > > >
> > > > > > > so the possible solution is store each RS position in a list
> > > > > > > at tx, and find the next RS from the list in
> > > > > > > ixgbe_dev_tx_descriptor_status
> > > > > > >
> > > > > > > If it is the second case, it will be simple we don't need to
> > > > > > > check forward with tx_rs_thresh, just check the exact
> > > > > > > position ( I hope it is this case :))
> > > > > >
> > > > > > In this patch, code "desc = txq->sw_ring[desc].last_id;" will
> > > > > > get the last index for several segments packet, that  solve
> > > > > > the case when packet contain more than one segment.
> > > > >
> > > > > Yes, but my understanding is we "set RS on the previous packet"
> > > > > but not the packet cross tx_rs_thresh boundary So even without
> > > > > multi-seg , it will be 30, 62, 94, but not 31, 63, 95, probably
> > > > > the reason we didn't see the issue, is because if we test it
> > > > > with
> > > > > 32 burst, the latest packet still will be set RS, so it will be
> > > > > 30,31, 62,63, 94, 95, but if we tested with 64 burst, I assume
> > > > > it will be 30,
> > 62, 63, 94 ... right?
> > > > >
> > > >
> > > > Update to last mail.
> > > > There are another RS bit set code, which set RS bit on last
> > > > descriptor of the threshold packet.
> > > > So, that is to say ixgbe_xmit_pkts() not only set 30 62 94, but also 31 63
> 95.
> > > > And it also set the last packet of the burst, so we do not need
> > > > fix this function, it is not bug.
> > > >
> > > > 		/* Set RS bit only on threshold packets' last descriptor */
> > > > 		if (txq->nb_tx_used >= txq->tx_rs_thresh) {
> > > > 			PMD_TX_FREE_LOG(DEBUG,
> > > > 					"Setting RS bit on TXD id="
> > > > 					"%4u (port=%d queue=%d)",
> > > > 					tx_last, txq->port_id, txq->queue_id);
> > > >
> > > > 			cmd_type_len |= IXGBE_TXD_CMD_RS;
> > > >
> > > > 			/* Update txq RS bit counters */
> > > > 			txq->nb_tx_used = 0;
> > > > 			txp = NULL;
> > > > 		}
> > >
> > > OK, but is this guarantee that slot 31, 63, 95 is always in the
> > > packet that cross tx_rx_thresh boundary?
> > > Let's assume every packet has 5 seg, so in every 7 packet the last
> > > one will cross the boundary.
> > > so it will be
> > > 0-4, 5-9, 10-14, 15-19, 20-24, 25-29, 30-34, 35-39, 40-44, 45-49,
> > > 50-54, 55-59, 60-64, 65-69 Definitely, it is possible that last
> > > packet (and the previous before
> > > last) does not include 32*n-1 In ixgbe_xmit_cleanup, it use
> > > desc_to_clean_to = sw_ring[desc_to_clean_to].last_id + tx_rx_thresh
> > > to calculate next packet in boundary, that's no problem But in
> > > ixgbe_dev_tx_descriptor_status, we assume the it is 31,63,95
> > > pattern, that
> > will be problem.
> >
> > In my patch for ixgbe_dev_tx_descriptor_status() We have code :
> >
> > 	desc = txq->sw_ring[desc].last_id;
> >  	status = &txq->tx_ring[desc].wb.status;
> >
> > it will only check last_id DD, if in the several segment case, it will
> > also to check the last DD.
> 
> Yes, but what I mean is we can't guarantee a packet cover 31, 63, 95 is the
> packet that cross tx_rs_thresh boundary,(whose last segment has RS).

Ok， I  will commit v2 for that.

> >
> > >
> > >
> > >
> > > >
> > > >
> > > > > >
> > > > > > >
> > > > > > > Regards
> > > > > > > Qi
> > > > > > > >
> > > > > > > > Fixes: a2919e13d95e ("net/ixgbe: implement descriptor
> > > > > > > > status
> > > > > > > > API")
> > > > > > > >
> > > > > > > > Signed-off-by: Wei Zhao <wei.zhao1@intel.com>
> > > > > > > > ---
> > > > > > > >  drivers/net/ixgbe/ixgbe_rxtx.c | 12 ++++++------
> > > > > > > >  1 file changed, 6 insertions(+), 6 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c
> > > > > > > > b/drivers/net/ixgbe/ixgbe_rxtx.c index 3e13d26..f185219
> > > > > > > > 100644
> > > > > > > > --- a/drivers/net/ixgbe/ixgbe_rxtx.c
> > > > > > > > +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
> > > > > > > > @@ -3146,15 +3146,15 @@
> > > > > > > > ixgbe_dev_tx_descriptor_status(void
> > > > > > > *tx_queue,
> > > > > > > > uint16_t offset)
> > > > > > > >  		return -EINVAL;
> > > > > > > >
> > > > > > > >  	desc = txq->tx_tail + offset;
> > > > > > > > +	if (desc >= txq->nb_tx_desc)
> > > > > > > > +		desc -= txq->nb_tx_desc;
> > > > > > > >  	/* go to next desc that has the RS bit */
> > > > > > > > -	desc = ((desc + txq->tx_rs_thresh - 1) / txq->tx_rs_thresh) *
> > > > > > > > -		txq->tx_rs_thresh;
> > > > > > > > -	if (desc >= txq->nb_tx_desc) {
> > > > > > > > +	desc = (desc  / txq->tx_rs_thresh + 1) *
> > > > > > > > +			txq->tx_rs_thresh - 1;
> > > > > > > > +	if (desc >= txq->nb_tx_desc)
> > > > > > > >  		desc -= txq->nb_tx_desc;
> > > > > > > > -		if (desc >= txq->nb_tx_desc)
> > > > > > > > -			desc -= txq->nb_tx_desc;
> > > > > > > > -	}
> > > > > > > >
> > > > > > > > +	desc = txq->sw_ring[desc].last_id;
> > > > > > > >  	status = &txq->tx_ring[desc].wb.status;
> > > > > > > >  	if (*status & rte_cpu_to_le_32(IXGBE_ADVTXD_STAT_DD))
> > > > > > > >  		return RTE_ETH_TX_DESC_DONE;
> > > > > > > > --
> > > > > > > > 2.7.5