linux-kernel - Re: [PATCH net-next v2 2/2] net: mvneta: Use cacheable memory to store the rx buffer DMA address

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Date:   Fri, 17 Feb 2017 14:30:03 +0100
From:   Gregory CLEMENT <gregory.clement@...e-electrons.com>
To:     Jisheng Zhang <jszhang@...vell.com>
Cc:     <thomas.petazzoni@...e-electrons.com>, <davem@...emloft.net>,
        <arnd@...db.de>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net-next v2 2/2] net: mvneta: Use cacheable memory to store the rx buffer DMA address

Hi Jisheng,

 On ven., févr. 17 2017, Jisheng Zhang <jszhang@...vell.com> wrote:

> In hot code path such as mvneta_rx_hwbm() and mvneta_rx_swbm, the
> buf_phys_addr field of rx_dec is accessed. The rx_desc is allocated by
> dma_alloc_coherent, it's uncacheable if the device isn't cache
> coherent, reading from uncached memory is fairly slow. This patch uses
> cacheable memory to store the rx buffer DMA address. We get the
> following performance data on Marvell BG4CT Platforms (tested with
> iperf):
>
> before the patch:
> recving 1GB in mvneta_rx_swbm() costs 1492659600 ns
>
> after the patch:
> recving 1GB in mvneta_rx_swbm() costs 1421565640 ns
>
> We saved 4.76% time.

I have just tested it and as I feared, with HWBM enabled, a simple iperf
just doesn't work.

Gregory

>
> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/net/ethernet/marvell/mvneta.c | 28 +++++++++++++++++-----------
>  1 file changed, 17 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index 06df72b8da85..e24c3028fe1d 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -580,6 +580,9 @@ struct mvneta_rx_queue {
>  	/* Virtual address of the RX buffer */
>  	void  **buf_virt_addr;
>  
> +	/* DMA address of the RX buffer */
> +	dma_addr_t *buf_dma_addr;
> +
>  	/* Virtual address of the RX DMA descriptors array */
>  	struct mvneta_rx_desc *descs;
>  
> @@ -1617,6 +1620,7 @@ static void mvneta_rx_desc_fill(struct mvneta_rx_desc *rx_desc,
>  
>  	rx_desc->buf_phys_addr = phys_addr;
>  	i = rx_desc - rxq->descs;
> +	rxq->buf_dma_addr[i] = phys_addr;
>  	rxq->buf_virt_addr[i] = virt_addr;
>  }
>  
> @@ -1900,22 +1904,22 @@ static void mvneta_rxq_drop_pkts(struct mvneta_port *pp,
>  		for (i = 0; i < rx_done; i++) {
>  			struct mvneta_rx_desc *rx_desc =
>  						  mvneta_rxq_next_desc_get(rxq);
> +			int index = rx_desc - rxq->descs;
>  			u8 pool_id = MVNETA_RX_GET_BM_POOL_ID(rx_desc->status);
>  			struct mvneta_bm_pool *bm_pool;
>  
>  			bm_pool = &pp->bm_priv->bm_pools[pool_id];
>  			/* Return dropped buffer to the pool */
>  			mvneta_bm_pool_put_bp(pp->bm_priv, bm_pool,
> -					      rx_desc->buf_phys_addr);
> +					      rxq->buf_dma_addr[index]);
>  		}
>  		return;
>  	}
>  
>  	for (i = 0; i < rxq->size; i++) {
> -		struct mvneta_rx_desc *rx_desc = rxq->descs + i;
>  		void *data = rxq->buf_virt_addr[i];
>  
> -		dma_unmap_single(pp->dev->dev.parent, rx_desc->buf_phys_addr,
> +		dma_unmap_single(pp->dev->dev.parent, rxq->buf_dma_addr[i],
>  				 MVNETA_RX_BUF_SIZE(pp->pkt_size), DMA_FROM_DEVICE);
>  		mvneta_frag_free(pp->frag_size, data);
>  	}
> @@ -1953,7 +1957,7 @@ static int mvneta_rx_swbm(struct mvneta_port *pp, int rx_todo,
>  		rx_bytes = rx_desc->data_size - (ETH_FCS_LEN + MVNETA_MH_SIZE);
>  		index = rx_desc - rxq->descs;
>  		data = rxq->buf_virt_addr[index];
> -		phys_addr = rx_desc->buf_phys_addr;
> +		phys_addr = rxq->buf_dma_addr[index];
>  
>  		if (!mvneta_rxq_desc_is_first_last(rx_status) ||
>  		    (rx_status & MVNETA_RXD_ERR_SUMMARY)) {
> @@ -2062,6 +2066,7 @@ static int mvneta_rx_hwbm(struct mvneta_port *pp, int rx_todo,
>  	/* Fairness NAPI loop */
>  	while (rx_done < rx_todo) {
>  		struct mvneta_rx_desc *rx_desc = mvneta_rxq_next_desc_get(rxq);
> +		int index = rx_desc - rxq->descs;
>  		struct mvneta_bm_pool *bm_pool = NULL;
>  		struct sk_buff *skb;
>  		unsigned char *data;
> @@ -2074,7 +2079,7 @@ static int mvneta_rx_hwbm(struct mvneta_port *pp, int rx_todo,
>  		rx_status = rx_desc->status;
>  		rx_bytes = rx_desc->data_size - (ETH_FCS_LEN + MVNETA_MH_SIZE);
>  		data = (u8 *)(uintptr_t)rx_desc->buf_cookie;
> -		phys_addr = rx_desc->buf_phys_addr;
> +		phys_addr = rxq->buf_dma_addr[index];
>  		pool_id = MVNETA_RX_GET_BM_POOL_ID(rx_status);
>  		bm_pool = &pp->bm_priv->bm_pools[pool_id];
>  
> @@ -2082,8 +2087,7 @@ static int mvneta_rx_hwbm(struct mvneta_port *pp, int rx_todo,
>  		    (rx_status & MVNETA_RXD_ERR_SUMMARY)) {
>  err_drop_frame_ret_pool:
>  			/* Return the buffer to the pool */
> -			mvneta_bm_pool_put_bp(pp->bm_priv, bm_pool,
> -					      rx_desc->buf_phys_addr);
> +			mvneta_bm_pool_put_bp(pp->bm_priv, bm_pool, phys_addr);
>  err_drop_frame:
>  			dev->stats.rx_errors++;
>  			mvneta_rx_error(pp, rx_desc);
> @@ -2098,7 +2102,7 @@ static int mvneta_rx_hwbm(struct mvneta_port *pp, int rx_todo,
>  				goto err_drop_frame_ret_pool;
>  
>  			dma_sync_single_range_for_cpu(dev->dev.parent,
> -			                              rx_desc->buf_phys_addr,
> +			                              phys_addr,
>  			                              MVNETA_MH_SIZE + NET_SKB_PAD,
>  			                              rx_bytes,
>  			                              DMA_FROM_DEVICE);
> @@ -2114,8 +2118,7 @@ static int mvneta_rx_hwbm(struct mvneta_port *pp, int rx_todo,
>  			rcvd_bytes += rx_bytes;
>  
>  			/* Return the buffer to the pool */
> -			mvneta_bm_pool_put_bp(pp->bm_priv, bm_pool,
> -					      rx_desc->buf_phys_addr);
> +			mvneta_bm_pool_put_bp(pp->bm_priv, bm_pool, phys_addr);
>  
>  			/* leave the descriptor and buffer untouched */
>  			continue;
> @@ -4019,7 +4022,10 @@ static int mvneta_init(struct device *dev, struct mvneta_port *pp)
>  		rxq->buf_virt_addr = devm_kmalloc(pp->dev->dev.parent,
>  						  rxq->size * sizeof(void *),
>  						  GFP_KERNEL);
> -		if (!rxq->buf_virt_addr)
> +		rxq->buf_dma_addr = devm_kmalloc(pp->dev->dev.parent,
> +						 rxq->size * sizeof(dma_addr_t),
> +						 GFP_KERNEL);
> +		if (!rxq->buf_virt_addr || !rxq->buf_dma_addr)
>  			return -ENOMEM;
>  	}
>  
> -- 
> 2.11.0
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com

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