Re: [dpdk-stable] [dpdk-dev] [PATCH v1] net/tap: fix blocked rx packets error

["Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>]

HI Marcin,

> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Marcin Smoczynski
> Sent: Monday, September 2, 2019 7:43 PM
> To: konstantin.ananyev@intel.com; keith.wiles@intel.com;
> adrien.mazarguil@6wind.com
> Cc: dev@dpdk.org; stable@dpdk.org; Marcin Smoczynski
> <marcinx.smoczynski@intel.com>; Mariusz Drost
> <mariuszx.drost@intel.com>
> Subject: [dpdk-dev] [PATCH v1] net/tap: fix blocked rx packets error
>
> When OS sends more packets than are beaing read with a single
s/ beaing/being

> 'rte_eth_rx_burst' call, rx packets are getting stucked in the tap pmd
> and are unable to receive, because trigger_seen is getting updated
> and consecutive calls are not getting any packets.
>
> Do not update trigger_seen unless less than a max number of packets were
> received allowing next call to receive the rest.
>
> Fixes: a0d8e807d9 ("net/tap: add Rx trigger")
> Cc: stable@dpdk.org
>
> Tested-by: Mariusz Drost <mariuszx.drost@intel.com>
> Signed-off-by: Marcin Smoczynski <marcinx.smoczynski@intel.com>
> ---
>  drivers/net/tap/rte_eth_tap.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
> index 64bd04911..60121ae56 100644
> --- a/drivers/net/tap/rte_eth_tap.c
> +++ b/drivers/net/tap/rte_eth_tap.c
> @@ -353,8 +353,7 @@ pmd_rx_burst(void *queue, struct rte_mbuf **bufs,
> uint16_t nb_pkts)
>
>       if (trigger == rxq->trigger_seen)
>               return 0;
> -     if (trigger)
> -             rxq->trigger_seen = trigger;
> +
>       process_private = rte_eth_devices[rxq->in_port].process_private;
>       rte_compiler_barrier();
I see this compiler barrier was added together with the above "rxq->trigger_seen = trigger", should it be removed or moved together downwards?

>       for (num_rx = 0; num_rx < nb_pkts; ) {
> @@ -433,6 +432,9 @@ pmd_rx_burst(void *queue, struct rte_mbuf **bufs,
> uint16_t nb_pkts)
>       rxq->stats.ipackets += num_rx;
>       rxq->stats.ibytes += num_rx_bytes;
>
> +     if (trigger && num_rx < nb_pkts)
> +             rxq->trigger_seen = trigger;
> +
>       return num_rx;
>  }
>
> --
> 2.17.1

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