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Commit 070e1f01 authored by Christophe Leroy's avatar Christophe Leroy Committed by David S. Miller
Browse files

net: fs_enet: don't unmap DMA when packet len is below copybreak 



When the length of the packet is below the defined copybreak limit,
the received packet is copied into a newly allocated skb in order
to reuse the skb. This is only interesting if it allow us to avoid
a new DMA mapping. We shall therefore not DMA unmap and remap the
skb->data. Instead, we invalidate the cache
with dma_sync_single_for_cpu() once the received data has been
copied into the new skb.

The following measures have been obtained on a mpc885 running at 132Mhz.
Measurement is done using the timebase with packets sent to the target
with 'ping -s 1' (packet len is 60):
* Without this patch: 182 TB ticks
* With this patch: 143 TB ticks

As a comparison, if we set the copybreak limit to 0, then we get
148 TB ticks. It means that without this patch, duration is even
worse when copying received data to a new skb instead of
allocating a new skb for next packet to be received

Signed-off-by: default avatarChristophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8572763a

drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c

+20 −16
Original line number Diff line number Diff line
@@ -226,21 +226,10 @@ static int fs_enet_napi(struct napi_struct *napi, int budget) 
			if (sc & BD_ENET_RX_OV)

				fep->stats.rx_crc_errors++;



			skb = fep->rx_skbuff[curidx];



			dma_unmap_single(fep->dev, CBDR_BUFADDR(bdp),

				L1_CACHE_ALIGN(PKT_MAXBUF_SIZE),

				DMA_FROM_DEVICE);



			skbn = skb;



			skbn = fep->rx_skbuff[curidx];

		} else {

			skb = fep->rx_skbuff[curidx];



			dma_unmap_single(fep->dev, CBDR_BUFADDR(bdp),

				L1_CACHE_ALIGN(PKT_MAXBUF_SIZE),

				DMA_FROM_DEVICE);



			/*

			 * Process the incoming frame.

			 */
@@ -256,12 +245,30 @@ static int fs_enet_napi(struct napi_struct *napi, int budget) 
					skb_copy_from_linear_data(skb,

						      skbn->data, pkt_len);

					swap(skb, skbn);

					dma_sync_single_for_cpu(fep->dev,

						CBDR_BUFADDR(bdp),

						L1_CACHE_ALIGN(pkt_len),

						DMA_FROM_DEVICE);

				}

			} else {

				skbn = netdev_alloc_skb(dev, ENET_RX_FRSIZE);



				if (skbn)

				if (skbn) {

					dma_addr_t dma;



					skb_align(skbn, ENET_RX_ALIGN);



					dma_unmap_single(fep->dev,

						CBDR_BUFADDR(bdp),

						L1_CACHE_ALIGN(PKT_MAXBUF_SIZE),

						DMA_FROM_DEVICE);



					dma = dma_map_single(fep->dev,

						skbn->data,

						L1_CACHE_ALIGN(PKT_MAXBUF_SIZE),

						DMA_FROM_DEVICE);

					CBDW_BUFADDR(bdp, dma);

				}

			}



			if (skbn != NULL) {
@@ -276,9 +283,6 @@ static int fs_enet_napi(struct napi_struct *napi, int budget) 
		}



		fep->rx_skbuff[curidx] = skbn;

		CBDW_BUFADDR(bdp, dma_map_single(fep->dev, skbn->data,

			     L1_CACHE_ALIGN(PKT_MAXBUF_SIZE),

			     DMA_FROM_DEVICE));

		CBDW_DATLEN(bdp, 0);

		CBDW_SC(bdp, (sc & ~BD_ENET_RX_STATS) | BD_ENET_RX_EMPTY);