Re: [dpdk-dev] [PATCH v2] net/i40e: add logic of processing continuous DD bits for Arm

[Joyce Kong <Joyce.Kong@arm.com>]

> -----Original Message-----
> From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Sent: Wednesday, June 30, 2021 9:15 AM
> To: Joyce Kong <Joyce.Kong@arm.com>; beilei.xing@intel.com;
> qi.z.zhang@intel.com; Ruifeng Wang <Ruifeng.Wang@arm.com>;
> bruce.richardson@intel.com; helin.zhang@intel.com
> Cc: dev@dpdk.org; stable@dpdk.org; nd <nd@arm.com>; Honnappa
> Nagarahalli <Honnappa.Nagarahalli@arm.com>; nd <nd@arm.com>
> Subject: RE: [PATCH v2] net/i40e: add logic of processing continuous DD bits
> for Arm
> 
> <snip>
> >
> > For Arm platforms, reading descs can get re-ordered, then the status
> > of DD bits will be discontinuous, so add the logic to only process
> > continuous descs by checking DD bits.
> >
> > Fixes: 4861cde46116 ("i40e: new poll mode driver")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > ---
> >  drivers/net/i40e/i40e_rxtx.c | 19 +++++++++++++++----
> >  1 file changed, 15 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/i40e/i40e_rxtx.c
> > b/drivers/net/i40e/i40e_rxtx.c index 6c58decec..86e2f083e 100644
> > --- a/drivers/net/i40e/i40e_rxtx.c
> > +++ b/drivers/net/i40e/i40e_rxtx.c
> > @@ -452,7 +452,7 @@ i40e_rx_scan_hw_ring(struct i40e_rx_queue *rxq)
> >  	uint16_t pkt_len;
> >  	uint64_t qword1;
> >  	uint32_t rx_status;
> > -	int32_t s[I40E_LOOK_AHEAD], nb_dd;
> > +	int32_t s[I40E_LOOK_AHEAD], var, nb_dd;
> >  	int32_t i, j, nb_rx = 0;
> >  	uint64_t pkt_flags;
> >  	uint32_t *ptype_tbl = rxq->vsi->adapter->ptype_tbl; @@ -482,11
> > +482,22 @@ i40e_rx_scan_hw_ring(struct i40e_rx_queue *rxq)
> >  					I40E_RXD_QW1_STATUS_SHIFT;
> >  		}
> >
> > -		rte_smp_rmb();
> > +		/* This barrier is to order loads of different words in the
> > descriptor */
> > +		rte_atomic_thread_fence(__ATOMIC_ACQUIRE);
> I think this should go into a separate commit as the following change is
> unrelated.

Will separate the two changes in v3.

> 
> >
> >  		/* Compute how many status bits were set */
> > -		for (j = 0, nb_dd = 0; j < I40E_LOOK_AHEAD; j++)
> > -			nb_dd += s[j] & (1 <<
> > I40E_RX_DESC_STATUS_DD_SHIFT);
> > +		for (j = 0, nb_dd = 0; j < I40E_LOOK_AHEAD; j++) {
> > +			var = s[j] & (1 << I40E_RX_DESC_STATUS_DD_SHIFT);
> > #ifdef
> > +RTE_ARCH_ARM
> > +			/* For Arm platforms, only compute continuous
> > status bits */
> > +			if (var)
> > +				nb_dd += 1;
> > +			else
> > +				break;
> > +#else
> > +			nb_dd += var;
> > +#endif
> > +		}
> >
> >  		nb_rx += nb_dd;
> >
> > --
> > 2.17.1