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

Started byJisheng Zhang <jszhang@marvell.com>
First post2017-02-17 11:20 +0100
Last post2017-02-17 16:30 +0100
Articles 4 — 3 participants

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  [PATCH net-next v2 2/2] net: mvneta: Use cacheable memory to store the rx buffer DMA address Jisheng Zhang <jszhang@marvell.com> - 2017-02-17 11:20 +0100
    Re: [PATCH net-next v2 2/2] net: mvneta: Use cacheable memory to store the rx buffer DMA address Gregory CLEMENT <gregory.clement@free-electrons.com> - 2017-02-17 14:40 +0100
      Re: [PATCH net-next v2 2/2] net: mvneta: Use cacheable memory to  store the rx buffer DMA address Thomas Petazzoni <thomas.petazzoni@free-electrons.com> - 2017-02-17 15:00 +0100
        Re: [PATCH net-next v2 2/2] net: mvneta: Use cacheable memory to store the rx buffer DMA address Gregory CLEMENT <gregory.clement@free-electrons.com> - 2017-02-17 16:30 +0100

#1583291 — [PATCH net-next v2 2/2] net: mvneta: Use cacheable memory to store the rx buffer DMA address

FromJisheng Zhang <jszhang@marvell.com>
Date2017-02-17 11:20 +0100
Subject[PATCH net-next v2 2/2] net: mvneta: Use cacheable memory to store the rx buffer DMA address
Message-ID<tbNNT-30z-1@gated-at.bofh.it>
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.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Suggested-by: Arnd Bergmann <arnd@arndb.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

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#1583408

FromGregory CLEMENT <gregory.clement@free-electrons.com>
Date2017-02-17 14:40 +0100
Message-ID<tbQVs-4RP-15@gated-at.bofh.it>
In reply to#1583291
Hi Jisheng,
 
 On ven., févr. 17 2017, Jisheng Zhang <jszhang@marvell.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@marvell.com>
> Suggested-by: Arnd Bergmann <arnd@arndb.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@lists.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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#1583418 — Re: [PATCH net-next v2 2/2] net: mvneta: Use cacheable memory to store the rx buffer DMA address

FromThomas Petazzoni <thomas.petazzoni@free-electrons.com>
Date2017-02-17 15:00 +0100
SubjectRe: [PATCH net-next v2 2/2] net: mvneta: Use cacheable memory to store the rx buffer DMA address
Message-ID<tbReN-4Z1-1@gated-at.bofh.it>
In reply to#1583408
Hello,

On Fri, 17 Feb 2017 14:30:03 +0100, Gregory CLEMENT wrote:

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

And that's expected: the whole point of HWBM is that the buffer into
which a RX packet is placed is allocated by the HW, and its address
stored in the RX descriptor. So the following code:

> >  	rx_desc->buf_phys_addr = phys_addr;
> >  	i = rx_desc - rxq->descs;
> > +	rxq->buf_dma_addr[i] = phys_addr;

Does not make sense, because it's not the SW that refills the RX
descriptors with the address of the RX buffers. It's done by the HW.

With HWBM, I believe you have no choice but to read the physical
address from the RX descriptor. But you can probably optimize things a
little bit by reading it only once, and then storing it into a
cacheable variable.

So maybe:

 - For SWBM, use the strategy proposed by Jisheng
 - For HWBM, at the beginning of the RX completion path, read once the
   rx_desc->buf_phys_addr, and store it in rxq->buf_dma_addr[index]

Of course that's just a very rough proposal. I've been looking mainly
at mvpp2 lately, and I'm not sure I still remember how mvneta works in
the details.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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#1583528

FromGregory CLEMENT <gregory.clement@free-electrons.com>
Date2017-02-17 16:30 +0100
Message-ID<tbSDU-60B-19@gated-at.bofh.it>
In reply to#1583418
Hi Thomas,
 
 On ven., févr. 17 2017, Thomas Petazzoni <thomas.petazzoni@free-electrons.com> wrote:

> Does not make sense, because it's not the SW that refills the RX
> descriptors with the address of the RX buffers. It's done by the HW.
>
> With HWBM, I believe you have no choice but to read the physical
> address from the RX descriptor. But you can probably optimize things a
> little bit by reading it only once, and then storing it into a
> cacheable variable.
>
> So maybe:
>
>  - For SWBM, use the strategy proposed by Jisheng
>  - For HWBM, at the beginning of the RX completion path, read once the
>    rx_desc->buf_phys_addr, and store it in rxq->buf_dma_addr[index]


For the HWBM path storing rx_desc->buf_phys_addr in
rxq->buf_dma_addr[index] is not useful as we only use it in a single
function.

But a quick improvement could be to use the phys_addr variable. Indeed
we store the value of rx_desc->buf_phys_addr in it and we never used it,
instead we always use rx_desc->buf_phys_addr.

Gregory

>
> Of course that's just a very rough proposal. I've been looking mainly
> at mvpp2 lately, and I'm not sure I still remember how mvneta works in
> the details.
>
> Best regards,
>
> Thomas
> -- 
> Thomas Petazzoni, CTO, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com

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

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