Re: [PATCH v4] net/i40e: fix Rx instability with vector mode

["Zhang, Qi Z" <qi.z.zhang@intel.com>]

> -----Original Message-----
> From: Ananyev, Konstantin
> Sent: Monday, November 5, 2018 4:05 AM
> To: Xing, Beilei <beilei.xing@intel.com>; Zhang, Qi Z <qi.z.zhang@intel.com>
> Cc: dev@dpdk.org; stable@dpdk.org
> Subject: RE: [PATCH v4] net/i40e: fix Rx instability with vector mode
> 
> 
> >
> > Previously, there is instability during vector Rx if descriptor number
> > is not power of 2, e.g. process hang and some Rx packets are
> > unexpectedly empty. That's because vector Rx mode assumes Rx
> > descriptor number is power of 2 when doing bit mask.
> > This patch allows vector mode only when the number of Rx descriptor is
> > power of 2.
> >
> > Fixes: 8e109464c022 ("i40e: allow vector Rx and Tx usage")
> > Fixes: a3c83a2527e1 ("net/i40e: enable runtime queue setup")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Beilei Xing <beilei.xing@intel.com>
> > ---
> > v4 changes:
> >  - Configure rx_vec_allowed in i40e_rx_vec_dev_conf_condition_check
> function.
> > v3 changes:
> >  - Add branch for non-first queue during runtime queue setup.
> >  - Use function rte_is_power_of_2().
> >  - Configure rx_vec_allowed during setting Rx function.
> > v2 changes:
> >  - rx_vec_allowed is global configuration, avoid overwrite.
> >
> >  doc/guides/nics/i40e.rst                |  7 ++++++
> >  drivers/net/i40e/i40e_rxtx.c            |  5 +++++
> >  drivers/net/i40e/i40e_rxtx_vec_common.h | 38
> > +++++++++++++++++++++++++++++++++
> >  3 files changed, 50 insertions(+)
> >
> > diff --git a/doc/guides/nics/i40e.rst b/doc/guides/nics/i40e.rst index
> > ab3928a..bfacbd1 100644
> > --- a/doc/guides/nics/i40e.rst
> > +++ b/doc/guides/nics/i40e.rst
> > @@ -172,6 +172,13 @@ Runtime Config Options
> >
> >    -w 84:00.0,use-latest-supported-vec=1
> >
> > +Vector RX Pre-conditions
> > +~~~~~~~~~~~~~~~~~~~~~~~~
> > +For Vector RX it is assumed that the number of descriptor rings will
> > +be a power of 2. With this pre-condition, the ring pointer can easily
> > +scroll back to the head after hitting the tail without a conditional
> > +check. In addition Vector RX can use this assumption to do a bit mask
> using ``ring_size - 1``.
> > +
> >  Driver compilation and testing
> >  ------------------------------
> >
> > diff --git a/drivers/net/i40e/i40e_rxtx.c
> > b/drivers/net/i40e/i40e_rxtx.c index a827456..5bb1a3c 100644
> > --- a/drivers/net/i40e/i40e_rxtx.c
> > +++ b/drivers/net/i40e/i40e_rxtx.c
> > @@ -1741,6 +1741,11 @@ i40e_dev_rx_queue_setup_runtime(struct
> rte_eth_dev *dev,
> >  			ad->rx_bulk_alloc_allowed = false;
> >  		i40e_set_rx_function(dev);
> >  		return 0;
> > +	} else if (ad->rx_vec_allowed && !rte_is_power_of_2(rxq->nb_rx_desc))
> {
> > +		PMD_DRV_LOG(ERR, "Vector mode is allowed, but descriptor"
> > +			    " number %d of queue %d isn't power of 2",
> > +			    rxq->nb_rx_desc, rxq->queue_id);
> > +		return -EINVAL;
> >  	}
> >
> >  	/* check bulk alloc conflict */
> > diff --git a/drivers/net/i40e/i40e_rxtx_vec_common.h
> > b/drivers/net/i40e/i40e_rxtx_vec_common.h
> > index f00f6d6..0e6ffa0 100644
> > --- a/drivers/net/i40e/i40e_rxtx_vec_common.h
> > +++ b/drivers/net/i40e/i40e_rxtx_vec_common.h
> > @@ -192,8 +192,13 @@ static inline int
> > i40e_rx_vec_dev_conf_condition_check_default(struct rte_eth_dev *dev)
> > {  #ifndef RTE_LIBRTE_IEEE1588
> > +	struct i40e_adapter *ad =
> > +		I40E_DEV_PRIVATE_TO_ADAPTER(dev->data->dev_private);
> >  	struct rte_eth_rxmode *rxmode = &dev->data->dev_conf.rxmode;
> >  	struct rte_fdir_conf *fconf = &dev->data->dev_conf.fdir_conf;
> > +	struct i40e_rx_queue *rxq;
> > +	uint16_t desc, i;
> > +	bool first_queue;
> >
> >  	/* no fdir support */
> >  	if (fconf->mode != RTE_FDIR_MODE_NONE) @@ -207,6 +212,39 @@
> > i40e_rx_vec_dev_conf_condition_check_default(struct rte_eth_dev *dev)
> >  	if (rxmode->offloads & DEV_RX_OFFLOAD_VLAN_EXTEND)
> >  		return -1;
> >
> > +	/**
> > +	 * Vector mode is allowed only when number of Rx queue
> > +	 * descriptor is power of 2.
> > +	 */
> > +	if (!dev->data->dev_started) {
> > +		first_queue = true;
> > +		for (i = 0; i < dev->data->nb_rx_queues; i++) {
> > +			rxq = dev->data->rx_queues[i];
> > +			if (!rxq)
> > +				continue;
> > +			desc = rxq->nb_rx_desc;
> > +			if (first_queue)
> > +				ad->rx_vec_allowed =
> > +					rte_is_power_of_2(desc);
> > +			else
> > +				ad->rx_vec_allowed =
> > +					ad->rx_vec_allowed ?
> > +					rte_is_power_of_2(desc) :
> > +					ad->rx_vec_allowed;
> > +			first_queue = false;
> > +		}
> > +	} else {
> > +		/* Only check the first queue's descriptor number */
> > +		for (i = 0; i < dev->data->nb_rx_queues; i++) {
> > +			rxq = dev->data->rx_queues[i];
> > +			if (!rxq)
> > +				continue;
> > +			desc = rxq->nb_rx_desc;
> > +			ad->rx_vec_allowed = rte_is_power_of_2(desc);
> > +			break;
> > +		}
> > +	}
> > +
> >  	return 0;
> >  #else
> >  	RTE_SET_USED(dev);
> > --
> 
> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

Applied to dpdk-next-net-intel.

Thanks
Qi

> 
> > 2.5.5