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: Christophe Leroy <christophe.le...@c-s.fr>
---
.../net/ethernet/freescale/fs_enet/fs_enet-main.c | 36 ++++++++++++----------
1 file changed, 20 insertions(+), 16 deletions(-)
diff --git a/drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c
b/drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c
index 7cd3ef9..addcae6 100644
--- a/drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c
+++ b/drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c
@@ -221,21 +221,10 @@ 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.
*/
@@ -251,12 +240,30 @@ 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) {
@@ -271,9 +278,6 @@ 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);
--
2.1.0
