| Message ID | 20131202095255.GA13247@linutronix.de |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Data: Monday, December 02, 2013 5:53 PM >To: Duan Fugang-B38611 >Cc: netdev@vger.kernel.org; David S. Miller; Estevam Fabio-R49496; Frank Li; >Jim Baxter; Marek Szyprowski >Subject: [PATCH v2] net: fec_main: dma_map() only the length of the skb > >On tx submit the driver always dma_map_single() FEC_ENET_TX_FRSIZE (=2048) >bytes. This works because we don't overwrite any memory after the data buffer, >we remove it from cache if it was there. So we hurt performace in case the >mapping of a smaller area makes a difference. >There is also a bug: If the data area starts shortly before the end of RAM say >0xc7fffa10 and the RAM ends at 0xc8000000 then we have enough space to fit the >data area (according to skb->len) but we would map beyond end of ram if we are >using 2048. In v2.6.31 (against which kernel this patch >made) there is the following check in dma_cache_maint(): > >|BUG_ON(!virt_addr_valid(start) || !virt_addr_valid(start + size - 1)); > >Since the area starting at 0xc8000000 is no longer virt_addr_valid() we >BUG() during dma_map_single(). The BUG() statement was removed in v3.5-rc1 as >per 2dc6a016 ("ARM: dma-mapping: use asm-generic/dma-mapping-common.h"). > >This patch was tested on v2.6.31 and then forward-ported and compile tested >only against the net tree. I think it is still worth fixing mainline even after >the BUG() statement is gone. > >Tested-by: Fugang Duan <B38611@freescale.com> >Cc: Marek Szyprowski <m.szyprowski@samsung.com> >Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> >--- >v1..v2: removed a blank line. > > drivers/net/ethernet/freescale/fec_main.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > >diff --git a/drivers/net/ethernet/freescale/fec_main.c >b/drivers/net/ethernet/freescale/fec_main.c >index 4cbebf3..73b000d 100644 >--- a/drivers/net/ethernet/freescale/fec_main.c >+++ b/drivers/net/ethernet/freescale/fec_main.c >@@ -385,7 +385,7 @@ fec_enet_start_xmit(struct sk_buff *skb, struct net_device >*ndev) > * data. > */ > bdp->cbd_bufaddr = dma_map_single(&fep->pdev->dev, bufaddr, >- FEC_ENET_TX_FRSIZE, DMA_TO_DEVICE); >+ skb->len, DMA_TO_DEVICE); > if (dma_mapping_error(&fep->pdev->dev, bdp->cbd_bufaddr)) { > bdp->cbd_bufaddr = 0; > fep->tx_skbuff[index] = NULL; >@@ -779,11 +779,10 @@ fec_enet_tx(struct net_device *ndev) > else > index = bdp - fep->tx_bd_base; > >- dma_unmap_single(&fep->pdev->dev, bdp->cbd_bufaddr, >- FEC_ENET_TX_FRSIZE, DMA_TO_DEVICE); >- bdp->cbd_bufaddr = 0; >- > skb = fep->tx_skbuff[index]; >+ dma_unmap_single(&fep->pdev->dev, bdp->cbd_bufaddr, skb->len, >+ DMA_TO_DEVICE); >+ bdp->cbd_bufaddr = 0; > > /* Check for errors. */ > if (status & (BD_ENET_TX_HB | BD_ENET_TX_LC | >-- >1.8.4.4 > Acked-by: Fugang Duan <B38611@freescale.com>
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Date: Mon, 2 Dec 2013 10:52:55 +0100 > On tx submit the driver always dma_map_single() FEC_ENET_TX_FRSIZE (=2048) > bytes. This works because we don't overwrite any memory after the data buffer, > we remove it from cache if it was there. So we hurt performace in case the > mapping of a smaller area makes a difference. > There is also a bug: If the data area starts shortly before the end of > RAM say 0xc7fffa10 and the RAM ends at 0xc8000000 then we have enough > space to fit the data area (according to skb->len) but we would map beyond > end of ram if we are using 2048. In v2.6.31 (against which kernel this patch > made) there is the following check in dma_cache_maint(): > > |BUG_ON(!virt_addr_valid(start) || !virt_addr_valid(start + size - 1)); > > Since the area starting at 0xc8000000 is no longer virt_addr_valid() we > BUG() during dma_map_single(). The BUG() statement was removed in v3.5-rc1 as > per 2dc6a016 ("ARM: dma-mapping: use asm-generic/dma-mapping-common.h"). > > This patch was tested on v2.6.31 and then forward-ported and compile > tested only against the net tree. I think it is still worth fixing > mainline even after the BUG() statement is gone. > > Tested-by: Fugang Duan <B38611@freescale.com> > Cc: Marek Szyprowski <m.szyprowski@samsung.com> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Applied, thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c index 4cbebf3..73b000d 100644 --- a/drivers/net/ethernet/freescale/fec_main.c +++ b/drivers/net/ethernet/freescale/fec_main.c @@ -385,7 +385,7 @@ fec_enet_start_xmit(struct sk_buff *skb, struct net_device *ndev) * data. */ bdp->cbd_bufaddr = dma_map_single(&fep->pdev->dev, bufaddr, - FEC_ENET_TX_FRSIZE, DMA_TO_DEVICE); + skb->len, DMA_TO_DEVICE); if (dma_mapping_error(&fep->pdev->dev, bdp->cbd_bufaddr)) { bdp->cbd_bufaddr = 0; fep->tx_skbuff[index] = NULL; @@ -779,11 +779,10 @@ fec_enet_tx(struct net_device *ndev) else index = bdp - fep->tx_bd_base; - dma_unmap_single(&fep->pdev->dev, bdp->cbd_bufaddr, - FEC_ENET_TX_FRSIZE, DMA_TO_DEVICE); - bdp->cbd_bufaddr = 0; - skb = fep->tx_skbuff[index]; + dma_unmap_single(&fep->pdev->dev, bdp->cbd_bufaddr, skb->len, + DMA_TO_DEVICE); + bdp->cbd_bufaddr = 0; /* Check for errors. */ if (status & (BD_ENET_TX_HB | BD_ENET_TX_LC |
On tx submit the driver always dma_map_single() FEC_ENET_TX_FRSIZE (=2048) bytes. This works because we don't overwrite any memory after the data buffer, we remove it from cache if it was there. So we hurt performace in case the mapping of a smaller area makes a difference. There is also a bug: If the data area starts shortly before the end of RAM say 0xc7fffa10 and the RAM ends at 0xc8000000 then we have enough space to fit the data area (according to skb->len) but we would map beyond end of ram if we are using 2048. In v2.6.31 (against which kernel this patch made) there is the following check in dma_cache_maint(): |BUG_ON(!virt_addr_valid(start) || !virt_addr_valid(start + size - 1)); Since the area starting at 0xc8000000 is no longer virt_addr_valid() we BUG() during dma_map_single(). The BUG() statement was removed in v3.5-rc1 as per 2dc6a016 ("ARM: dma-mapping: use asm-generic/dma-mapping-common.h"). This patch was tested on v2.6.31 and then forward-ported and compile tested only against the net tree. I think it is still worth fixing mainline even after the BUG() statement is gone. Tested-by: Fugang Duan <B38611@freescale.com> Cc: Marek Szyprowski <m.szyprowski@samsung.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- v1..v2: removed a blank line. drivers/net/ethernet/freescale/fec_main.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)