Re: [dpdk-stable] [PATCH] eventdev: fix Rx adapter stalls on event device backpressure

["Mattias Rönnblom" <mattias.ronnblom@ericsson.com>]

On 2021-11-08 14:25, Mattias Rönnblom wrote:
> In the Eventdev Ethernet RX Adapter, correctly handle the case where
> the circular enqueue buffer head and tail index points to the same
> element (i.e., the buffer is full) and the buffer has wrapped.
>
> This bug may be triggered in case there is backpressure from the event
> device to the RX adapter.
>
> Fixes: 8113fd15e229 ("eventdev/eth_rx: make enqueue buffer circular")
> Cc: ganapati.kundapura@intel.com
> Cc: stable@dpdk.org


Disregard the stable cc. This bug does not appear in any released DPDK 
version (e.g., 21.08).


> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> ---
>   lib/eventdev/rte_event_eth_rx_adapter.c | 22 ++++++++++++++--------
>   1 file changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/lib/eventdev/rte_event_eth_rx_adapter.c b/lib/eventdev/rte_event_eth_rx_adapter.c
> index 56318b5a6f..809416d9b7 100644
> --- a/lib/eventdev/rte_event_eth_rx_adapter.c
> +++ b/lib/eventdev/rte_event_eth_rx_adapter.c
> @@ -777,19 +777,25 @@ rxa_flush_event_buffer(struct event_eth_rx_adapter *rx_adapter,
>   		       struct eth_event_enqueue_buffer *buf,
>   		       struct rte_event_eth_rx_adapter_stats *stats)
>   {
> -	uint16_t count = buf->last ? buf->last - buf->head : buf->count;
> +	uint16_t count = buf->count;
> +	uint16_t n = 0;
>   
>   	if (!count)
>   		return 0;
>   
> -	uint16_t n = rte_event_enqueue_new_burst(rx_adapter->eventdev_id,
> -					rx_adapter->event_port_id,
> -					&buf->events[buf->head],
> -					count);
> -	if (n != count)
> -		stats->rx_enq_retry++;
> +	if (buf->last)
> +		count = buf->last - buf->head;
> +
> +	if (count) {
> +		n = rte_event_enqueue_new_burst(rx_adapter->eventdev_id,
> +						rx_adapter->event_port_id,
> +						&buf->events[buf->head],
> +						count);
> +		if (n != count)
> +			stats->rx_enq_retry++;
>   
> -	buf->head += n;
> +		buf->head += n;
> +	}
>   
>   	if (buf->last && n == count) {
>   		uint16_t n1;