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Date: Sun, 14 Apr 2024 14:21:23 +0200
From: Niklas =?utf-8?Q?S=C3=B6derlund?= <niklas.soderlund+renesas@ragnatech.se>
To: Paul Barker <paul.barker.ct@bp.renesas.com>
Cc: Sergey Shtylyov <s.shtylyov@omp.ru>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>,
	Biju Das <biju.das.jz@bp.renesas.com>,
	YueHaibing <yuehaibing@huawei.com>, netdev@vger.kernel.org,
	linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [net PATCH v2 1/4] net: ravb: Count packets instead of
 descriptors in R-Car RX path
Message-ID: <20240414122123.GC2860391@ragnatech.se>
References: <20240412100024.2296-1-paul.barker.ct@bp.renesas.com>
 <20240412100024.2296-2-paul.barker.ct@bp.renesas.com>
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In-Reply-To: <20240412100024.2296-2-paul.barker.ct@bp.renesas.com>

Hi Paul,

Sorry I just posted my review comments on v1 of this series instead of 
v2. They where intended and are still valid for v2, sorry for the noise, 
let me know if you want me to repost them here.

On 2024-04-12 11:00:21 +0100, Paul Barker wrote:
> The units of "work done" in the RX path should be packets instead of
> descriptors.
> 
> Descriptors which are used by the hardware to record error conditions or
> are empty in the case of a DMA mapping error should not count towards
> our RX work budget.
> 
> Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
> Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
> Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
> ---
>  drivers/net/ethernet/renesas/ravb_main.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index ba01c8cc3c90..70f2900648d4 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -892,29 +892,25 @@ static bool ravb_rx_rcar(struct net_device *ndev, int *quota, int q)
>  	struct ravb_private *priv = netdev_priv(ndev);
>  	const struct ravb_hw_info *info = priv->info;
>  	int entry = priv->cur_rx[q] % priv->num_rx_ring[q];
> -	int boguscnt = (priv->dirty_rx[q] + priv->num_rx_ring[q]) -
> -			priv->cur_rx[q];
>  	struct net_device_stats *stats = &priv->stats[q];
>  	struct ravb_ex_rx_desc *desc;
>  	struct sk_buff *skb;
>  	dma_addr_t dma_addr;
>  	struct timespec64 ts;
> +	int rx_packets = 0;
>  	u8  desc_status;
>  	u16 pkt_len;
>  	int limit;
> +	int i;
>  
> -	boguscnt = min(boguscnt, *quota);
> -	limit = boguscnt;
> +	limit = priv->dirty_rx[q] + priv->num_rx_ring[q] - priv->cur_rx[q];
>  	desc = &priv->rx_ring[q].ex_desc[entry];
> -	while (desc->die_dt != DT_FEMPTY) {
> +	for (i = 0; i < limit && rx_packets < *quota && desc->die_dt != DT_FEMPTY; i++) {
>  		/* Descriptor type must be checked before all other reads */
>  		dma_rmb();
>  		desc_status = desc->msc;
>  		pkt_len = le16_to_cpu(desc->ds_cc) & RX_DS;
>  
> -		if (--boguscnt < 0)
> -			break;
> -
>  		/* We use 0-byte descriptors to mark the DMA mapping errors */
>  		if (!pkt_len)
>  			continue;
> @@ -960,7 +956,7 @@ static bool ravb_rx_rcar(struct net_device *ndev, int *quota, int q)
>  			if (ndev->features & NETIF_F_RXCSUM)
>  				ravb_rx_csum(skb);
>  			napi_gro_receive(&priv->napi[q], skb);
> -			stats->rx_packets++;
> +			rx_packets++;
>  			stats->rx_bytes += pkt_len;
>  		}
>  
> @@ -995,9 +991,9 @@ static bool ravb_rx_rcar(struct net_device *ndev, int *quota, int q)
>  		desc->die_dt = DT_FEMPTY;
>  	}
>  
> -	*quota -= limit - (++boguscnt);
> -
> -	return boguscnt <= 0;
> +	stats->rx_packets += rx_packets;
> +	*quota -= rx_packets;
> +	return *quota == 0;
>  }
>  
>  /* Packet receive function for Ethernet AVB */
> -- 
> 2.39.2
> 

-- 
Kind Regards,
Niklas Söderlund