netdev - Re: [PATCH net-next v5 2/2] net: ethernet: mediatek: enhance RX path by aggregating more SKBs into NAPI

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Date:   Wed, 7 Sep 2016 08:38:00 +0200
From:   John Crispin <john@...ozen.org>
To:     sean.wang@...iatek.com, davem@...emloft.net
Cc:     nbd@...nwrt.org, keyhaede@...il.com, netdev@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, objelf@...il.com
Subject: Re: [PATCH net-next v5 2/2] net: ethernet: mediatek: enhance RX path
 by aggregating more SKBs into NAPI



On 03/09/2016 11:59, sean.wang@...iatek.com wrote:
> From: Sean Wang <sean.wang@...iatek.com>
> 
> The patch adds support for aggregating more SKBs feed into NAPI in
> order to get more benefits from generic receive offload (GRO) by
> peeking at the RX ring status and moving more packets right before
> returning from NAPI RX polling handler if NAPI budgets are still
> available and some packets already present in hardware.
> 
> Signed-off-by: Sean Wang <sean.wang@...iatek.com>

this looks ok to me, gave it a quick try on my HW and it works well. i
am just not sure if this is something that is commonly done. someone
with more overview of how NAPI should be used might want to comment on this.

Tested-by: John Crispin <john@...ozen.org>


> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 31 ++++++++++++++++-------------
>  1 file changed, 17 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index a1bdb53..66fd45a 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -893,14 +893,14 @@ release_desc:
>  
>  		done++;
>  	}
> -	/* make sure that all changes to the dma ring are flushed before
> -	 * we continue
> -	 */
> -	wmb();
> -	mtk_w32(eth, ring->calc_idx, MTK_PRX_CRX_IDX0);
>  
> -	if (done < budget)
> -		mtk_w32(eth, MTK_RX_DONE_INT, MTK_PDMA_INT_STATUS);
> +	if (done) {
> +		/* make sure that all changes to the dma ring are flushed before
> +		 * we continue
> +		 */
> +		wmb();
> +		mtk_w32(eth, ring->calc_idx, MTK_PRX_CRX_IDX0);
> +	}
>  
>  	return done;
>  }
> @@ -1020,10 +1020,13 @@ static int mtk_napi_rx(struct napi_struct *napi, int budget)
>  	struct mtk_eth *eth = container_of(napi, struct mtk_eth, rx_napi);
>  	u32 status, mask;
>  	int rx_done = 0;
> +	int remain_budget = budget;
>  
>  	mtk_handle_status_irq(eth);
> +
> +poll_again:
>  	mtk_w32(eth, MTK_RX_DONE_INT, MTK_PDMA_INT_STATUS);
> -	rx_done = mtk_poll_rx(napi, budget, eth);
> +	rx_done = mtk_poll_rx(napi, remain_budget, eth);
>  
>  	if (unlikely(netif_msg_intr(eth))) {
>  		status = mtk_r32(eth, MTK_PDMA_INT_STATUS);
> @@ -1032,18 +1035,18 @@ static int mtk_napi_rx(struct napi_struct *napi, int budget)
>  			 "done rx %d, intr 0x%08x/0x%x\n",
>  			 rx_done, status, mask);
>  	}
> -
> -	if (rx_done == budget)
> +	if (rx_done == remain_budget)
>  		return budget;
>  
>  	status = mtk_r32(eth, MTK_PDMA_INT_STATUS);
> -	if (status & MTK_RX_DONE_INT)
> -		return budget;
> -
> +	if (status & MTK_RX_DONE_INT) {
> +		remain_budget -= rx_done;
> +		goto poll_again;
> +	}
>  	napi_complete(napi);
>  	mtk_irq_enable(eth, MTK_PDMA_INT_MASK, MTK_RX_DONE_INT);
>  
> -	return rx_done;
> +	return rx_done + budget - remain_budget;
>  }
>  
>  static int mtk_tx_alloc(struct mtk_eth *eth)
>