RE: [PATCH net v2] net: xilinx: axienet: Fix packet counting

[Pandey, Radhey Shyam]

> -----Original Message-----
> From: Sean Anderson <sean.anderson@xxxxxxxxx>
> Sent: Friday, September 6, 2024 10:12 PM
> To: Pandey, Radhey Shyam <radhey.shyam.pandey@xxxxxxx>; David S .
> Miller <davem@xxxxxxxxxxxxx>; Eric Dumazet <edumazet@xxxxxxxxxx>;
> Jakub Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni <pabeni@xxxxxxxxxx>;
> netdev@xxxxxxxxxxxxxxx
> Cc: Simek, Michal <michal.simek@xxxxxxx>; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Andy Chiu
> <andy.chiu@xxxxxxxxxx>; Daniel Borkmann <daniel@xxxxxxxxxxxxx>; Sean
> Anderson <sean.anderson@xxxxxxxxx>
> Subject: [PATCH net v2] net: xilinx: axienet: Fix packet counting
> 
> axienet_free_tx_chain returns the number of DMA descriptors it's
> handled. However, axienet_tx_poll treats the return as the number of
> packets. When scatter-gather SKBs are enabled, a single packet may use
> multiple DMA descriptors, which causes incorrect packet counts. Fix this
> by explicitly keepting track of the number of packets processed as
> separate from the DMA descriptors.
> 
> Fixes: 8a3b7a252dca ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet

Isn't it Fixes: 9e2bc267e780 ("net: axienet: Use NAPI for TX completion path")?

> driver")
> Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxxx>

+ Harini, Suraj to review and run this patch to ensure data path sanity.

> ---
> 
> Changes in v2:
> - Only call napi_consume_skb with non-zero budget when force is false
> 
>  .../net/ethernet/xilinx/xilinx_axienet_main.c | 31 +++++++++++--------
>  1 file changed, 18 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index 9aeb7b9f3ae4..556033849d55 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -670,21 +670,21 @@ static int axienet_device_reset(struct net_device
> *ndev)
>   * @force:	Whether to clean descriptors even if not complete
>   * @sizep:	Pointer to a u32 filled with the total sum of all bytes
>   *		in all cleaned-up descriptors. Ignored if NULL.
> - * @budget:	NAPI budget (use 0 when not called from NAPI poll)
> + * @budget:	NAPI budget (use INT_MAX when not called from NAPI poll)
>   *
>   * Would either be called after a successful transmit operation, or after
>   * there was an error when setting up the chain.
> - * Returns the number of descriptors handled.
> + * Returns the number of packets handled.
>   */
>  static int axienet_free_tx_chain(struct axienet_local *lp, u32 first_bd,
>  				 int nr_bds, bool force, u32 *sizep, int
> budget)
>  {
>  	struct axidma_bd *cur_p;
>  	unsigned int status;
> +	int i, packets = 0;
>  	dma_addr_t phys;
> -	int i;
> 
> -	for (i = 0; i < nr_bds; i++) {
> +	for (i = 0; i < nr_bds && packets < budget; i++) {
>  		cur_p = &lp->tx_bd_v[(first_bd + i) % lp->tx_bd_num];
>  		status = cur_p->status;
> 
> @@ -701,8 +701,10 @@ static int axienet_free_tx_chain(struct axienet_local
> *lp, u32 first_bd,
>  				 (cur_p->cntrl &
> XAXIDMA_BD_CTRL_LENGTH_MASK),
>  				 DMA_TO_DEVICE);
> 
> -		if (cur_p->skb && (status &
> XAXIDMA_BD_STS_COMPLETE_MASK))
> -			napi_consume_skb(cur_p->skb, budget);
> +		if (cur_p->skb && (status &
> XAXIDMA_BD_STS_COMPLETE_MASK)) {
> +			napi_consume_skb(cur_p->skb, force ? 0 : budget);
> +			packets++;
> +		}
> 
>  		cur_p->app0 = 0;
>  		cur_p->app1 = 0;
> @@ -718,7 +720,13 @@ static int axienet_free_tx_chain(struct axienet_local
> *lp, u32 first_bd,
>  			*sizep += status &
> XAXIDMA_BD_STS_ACTUAL_LEN_MASK;
>  	}
> 
> -	return i;
> +	if (!force) {

Is tx_bd_ci increment dependent on force state and not done if force == true ?
> +		lp->tx_bd_ci += i;
> +		if (lp->tx_bd_ci >= lp->tx_bd_num)
> +			lp->tx_bd_ci %= lp->tx_bd_num;
> +	}
> +
> +	return packets;
>  }
> 
>  /**
> @@ -891,13 +899,10 @@ static int axienet_tx_poll(struct napi_struct *napi,
> int budget)
>  	u32 size = 0;
>  	int packets;
> 
> -	packets = axienet_free_tx_chain(lp, lp->tx_bd_ci, budget, false,
> &size, budget);
> +	packets = axienet_free_tx_chain(lp, lp->tx_bd_ci, lp->tx_bd_num,

Why do we need to pass tx_bd_num here? Is budget not sufficient?

> false,
> +					&size, budget);
> 
>  	if (packets) {
> -		lp->tx_bd_ci += packets;
> -		if (lp->tx_bd_ci >= lp->tx_bd_num)
> -			lp->tx_bd_ci %= lp->tx_bd_num;
> -
>  		u64_stats_update_begin(&lp->tx_stat_sync);
>  		u64_stats_add(&lp->tx_packets, packets);
>  		u64_stats_add(&lp->tx_bytes, size);
> @@ -1003,7 +1008,7 @@ axienet_start_xmit(struct sk_buff *skb, struct
> net_device *ndev)
>  				netdev_err(ndev, "TX DMA mapping
> error\n");
>  			ndev->stats.tx_dropped++;
>  			axienet_free_tx_chain(lp, orig_tail_ptr, ii + 1,
> -					      true, NULL, 0);
> +					      true, NULL, INT_MAX);
>  			return NETDEV_TX_OK;
>  		}
>  		desc_set_phys_addr(lp, phys, cur_p);
> --
> 2.35.1.1320.gc452695387.dirty