Subject: Re: [PATCH net 3/6] igc: Fix TX Hang issue when QBV Gate is closed

From: Leon Romanovsky <[email-masked]>
Date: Thu, 6 Jul 2023 10:56:21 +0300

On Wed, Jul 05, 2023 at 01:19:02PM -0700, Tony Nguyen wrote:
> From: Muhammad Husaini Zulkifli <[email-masked]>
> 
> If a user schedules a Gate Control List (GCL) to close one of
> the QBV gates while also transmitting a packet to that closed gate,
> TX Hang will be happen. HW would not drop any packet when the gate
> is closed and keep queuing up in HW TX FIFO until the gate is re-opened.
> This patch implements the solution to drop the packet for the closed
> gate.
> 
> This patch will also reset the adapter to perform SW initialization
> for each 1st Gate Control List (GCL) to avoid hang.
> This is due to the HW design, where changing to TSN transmit mode
> requires SW initialization. Intel Discrete I225/6 transmit mode
> cannot be changed when in dynamic mode according to Software User
> Manual Section 7.5.2.1. Subsequent Gate Control List (GCL) operations
> will proceed without a reset, as they already are in TSN Mode.
> 
> Step to reproduce:
> 
> DUT:
> 1) Configure GCL List with certain gate close.
> 
> BASE=$(date +%s%N)
> tc qdisc replace dev $IFACE parent root handle 100 taprio \
>     num_tc 4 \
>     map 0 1 2 3 3 3 3 3 3 3 3 3 3 3 3 3 \
>     queues 1@0 1@1 1@2 1@3 \
>     base-time $BASE \
>     sched-entry S 0x8 500000 \
>     sched-entry S 0x4 500000 \
>     flags 0x2
> 
> 2) Transmit the packet to closed gate. You may use udp_tai
> application to transmit UDP packet to any of the closed gate.
> 
> ./udp_tai -i <interface> -P 100000 -p 90 -c 1 -t <0/1> -u 30004
> 
> Fixes: ec50a9d437f0 ("igc: Add support for taprio offloading")
> Co-developed-by: Tan Tee Min <[email-masked]>
> Signed-off-by: Tan Tee Min <[email-masked]>
> Tested-by: Chwee Lin Choong <[email-masked]>
> Signed-off-by: Muhammad Husaini Zulkifli <[email-masked]>
> Tested-by: Naama Meir <[email-masked]>
> Signed-off-by: Tony Nguyen <[email-masked]>
> ---
>  drivers/net/ethernet/intel/igc/igc.h      |  6 +++
>  drivers/net/ethernet/intel/igc/igc_main.c | 58 +++++++++++++++++++++--
>  drivers/net/ethernet/intel/igc/igc_tsn.c  | 41 ++++++++++------
>  3 files changed, 87 insertions(+), 18 deletions(-)

<...>

> @@ -6149,6 +6157,8 @@ static int igc_save_qbv_schedule(struct igc_adapter *adapter,
>  	adapter->cycle_time = qopt->cycle_time;
>  	adapter->base_time = qopt->base_time;
>  
> +	igc_ptp_read(adapter, &now);
> +
>  	for (n = 0; n < qopt->num_entries; n++) {
>  		struct tc_taprio_sched_entry *e = &qopt->entries[n];
>  
> @@ -6183,7 +6193,10 @@ static int igc_save_qbv_schedule(struct igc_adapter *adapter,
>  				ring->start_time = start_time;
>  			ring->end_time = end_time;
>  
> -			queue_configured[i] = true;
> +			if (ring->start_time >= adapter->cycle_time)
> +				queue_configured[i] = false;
> +			else
> +				queue_configured[i] = true;
>  		}
>  
>  		start_time += e->interval;
> @@ -6193,8 +6206,20 @@ static int igc_save_qbv_schedule(struct igc_adapter *adapter,
>  	 * If not, set the start and end time to be end time.
>  	 */
>  	for (i = 0; i < adapter->num_tx_queues; i++) {
> +		struct igc_ring *ring = adapter->tx_ring[i];
> +
> +		if (!is_base_time_past(qopt->base_time, &now)) {
> +			ring->admin_gate_closed = false;
> +		} else {
> +			ring->oper_gate_closed = false;
> +			ring->admin_gate_closed = false;
> +		}
> +
>  		if (!queue_configured[i]) {
> -			struct igc_ring *ring = adapter->tx_ring[i];
> +			if (!is_base_time_past(qopt->base_time, &now))
> +				ring->admin_gate_closed = true;
> +			else
> +				ring->oper_gate_closed = true;
>  
>  			ring->start_time = end_time;
>  			ring->end_time = end_time;
> @@ -6575,6 +6600,27 @@ static const struct xdp_metadata_ops igc_xdp_metadata_ops = {
>  	.xmo_rx_timestamp		= igc_xdp_rx_timestamp,
>  };
>  
> +static enum hrtimer_restart igc_qbv_scheduling_timer(struct hrtimer *timer)
> +{
> +	struct igc_adapter *adapter = container_of(timer, struct igc_adapter,
> +						   hrtimer);
> +	unsigned int i;
> +
> +	adapter->qbv_transition = true;
> +	for (i = 0; i < adapter->num_tx_queues; i++) {
> +		struct igc_ring *tx_ring = adapter->tx_ring[i];
> +
> +		if (tx_ring->admin_gate_closed) {

Doesn't asynchronic access to shared variable through hrtimer require some sort of locking?

Thanks

> +			tx_ring->admin_gate_closed = false;
> +			tx_ring->oper_gate_closed = true;
> +		} else {
> +			tx_ring->oper_gate_closed = false;
> +		}
> +	}
> +	adapter->qbv_transition = false;
> +	return HRTIMER_NORESTART;
> +}
> +