netdev - Re: [PATCH net-next v5 1/2] net: ethernet: mediatek: enhance RX path by reducing the frequency of the memory barrier used

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Date:   Wed, 7 Sep 2016 08:35:32 +0200
From:   John Crispin <john@...ozen.org>
To:     sean.wang@...iatek.com, davem@...emloft.net
Cc:     nbd@...nwrt.org, netdev@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, keyhaede@...il.com,
        objelf@...il.com
Subject: Re: [PATCH net-next v5 1/2] net: ethernet: mediatek: enhance RX path
 by reducing the frequency of the memory barrier used



On 03/09/2016 11:59, sean.wang@...iatek.com wrote:
> From: Sean Wang <sean.wang@...iatek.com>
> 
> The patch makes move wmb() to outside the loop that could help
> RX path handling more faster although that RX descriptors aren't
> freed for DMA to use as soon as possible, but based on my experiment
> and the result shows it still can reach about 943Mbpis without
> performance drop that is tested based on the setup with one port
> using Giga PHY and 256 RX descriptors for DMA to move.
> 
> Signed-off-by: Sean Wang <sean.wang@...iatek.com>

gave it a quick spin on my hardware and it works well even when using
more than 1 gmac.

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

> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index 431b851..a1bdb53 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -890,13 +890,14 @@ release_desc:
>  		rxd->rxd2 = RX_DMA_PLEN0(ring->buf_size);
>  
>  		ring->calc_idx = idx;
> -		/* 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);
> +
>  		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);
>