pch_gbe: dont-copy-payload (was [PATCH 1/4] ...)

Submitted by Andy Cress on Aug. 6, 2012, 2:19 p.m.

Details

Message ID 40680C535D6FE6498883F1640FACD44D0122CF12@ka-exchange-1.kontronamerica.local
State RFC
Delegated to: David Miller
Headers show

Commit Message

Andy Cress Aug. 6, 2012, 2:19 p.m.
I found out why the proposed dont-copy-payload patch didn't work with this pch_gbe NIC.
This NIC PHY requires 64-byte-aligned DMA, and the transmit buffers won't be transferred if skb->data is not 64-byte-aligned.  Apparently the data copy has a by-product of aligning the buffers.  

I tried using skb_reserve(skb,64) in pch_gbe_alloc_tx_buffers and pch-gbe_alloc_rx_buffers, but that didn't seem to resolve it.

How can I make sure that the transmit data buffers are 64-byte-aligned?

Andy

-----Original Message-----
From: Andy Cress

Sent: Wednesday, July 25, 2012 4:11 PM
Subject: RE: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[...]
I tried applying the dont-copy-payload patch you outlined below, and for some reason it won't send successfully with that change.   I'm not sure why though.  This approach seems sound, and should greatly help transmit performance, if I could figure out what else it needs.  

Andy

-----Original Message-----
From: Eric Dumazet 

Sent: Tuesday, July 17, 2012 3:33 AM
To: Andy Cress
Cc: netdev@vger.kernel.org; Zhong Hongbo
Subject: Re: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

On Tue, 2012-07-17 at 09:09 +0200, Eric Dumazet wrote:
[...]
> There _must_ be a way to avoid most of these copies (ie not touching

> payload), only mess with the header to insert these 2 nul bytes ?

> 

> /* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */

[...]

Something like the following (untested) patch


 drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c |   55 +++++-----
 1 file changed, 29 insertions(+), 26 deletions(-)

Comments

Eric Dumazet Aug. 6, 2012, 2:52 p.m.
On Mon, 2012-08-06 at 07:19 -0700, Andy Cress wrote:
> I found out why the proposed dont-copy-payload patch didn't work with
> this pch_gbe NIC.
> This NIC PHY requires 64-byte-aligned DMA, and the transmit buffers
> won't be transferred if skb->data is not 64-byte-aligned.  Apparently
> the data copy has a by-product of aligning the buffers.  
> 
> I tried using skb_reserve(skb,64) in pch_gbe_alloc_tx_buffers and
> pch-gbe_alloc_rx_buffers, but that didn't seem to resolve it.
> 
> How can I make sure that the transmit data buffers are
> 64-byte-aligned?
> 

There is no support for such requirement in linux stacks.

Only solution for the driver is to copy all frames to 64-byte-aligned
bounce buffers.



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Patch hide | download patch | download mbox

diff --git a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
index b100656..2d3d982 100644
--- a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
+++ b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
@@ -1163,7 +1163,7 @@  static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 	struct pch_gbe_hw *hw = &adapter->hw;
 	struct pch_gbe_tx_desc *tx_desc;
 	struct pch_gbe_buffer *buffer_info;
-	struct sk_buff *tmp_skb;
+	char *ptr;
 	unsigned int frame_ctrl;
 	unsigned int ring_num;
 
@@ -1221,18 +1221,27 @@  static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 
 
 	buffer_info = &tx_ring->buffer_info[ring_num];
-	tmp_skb = buffer_info->skb;
+	if (skb_headroom(skb) < 2) {
+		struct sk_buff *skb_new;
+
+		skb_new = skb_realloc_headroom(skb, 2);
+		if (!skb_new) {
+			tx_ring->next_to_use = ring_num;
+			dev_kfree_skb_any(skb);
+			return;
+		}
+		consume_skb(skb);
+		skb = skb_new;
+	}
 
 	/* [Header:14][payload] ---> [Header:14][paddong:2][payload]    */
-	memcpy(tmp_skb->data, skb->data, ETH_HLEN);
-	tmp_skb->data[ETH_HLEN] = 0x00;
-	tmp_skb->data[ETH_HLEN + 1] = 0x00;
-	tmp_skb->len = skb->len;
-	memcpy(&tmp_skb->data[ETH_HLEN + 2], &skb->data[ETH_HLEN],
-	       (skb->len - ETH_HLEN));
+	ptr = skb_push(skb, 2);
+	memmove(ptr, ptr + 2, ETH_HLEN);
+	ptr[ETH_HLEN] = 0x00;
+	ptr[ETH_HLEN + 1] = 0x00;
 	/*-- Set Buffer information --*/
-	buffer_info->length = tmp_skb->len;
-	buffer_info->dma = dma_map_single(&adapter->pdev->dev, tmp_skb->data,
+	buffer_info->length = skb->len;
+	buffer_info->dma = dma_map_single(&adapter->pdev->dev, skb->data,
 					  buffer_info->length,
 					  DMA_TO_DEVICE);
 	if (dma_mapping_error(&adapter->pdev->dev, buffer_info->dma)) {
@@ -1240,18 +1249,20 @@  static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 		buffer_info->dma = 0;
 		buffer_info->time_stamp = 0;
 		tx_ring->next_to_use = ring_num;
+		dev_kfree_skb_any(skb);
 		return;
 	}
 	buffer_info->mapped = true;
 	buffer_info->time_stamp = jiffies;
+	buffer_info->skb = skb;
 
 	/*-- Set Tx descriptor --*/
 	tx_desc = PCH_GBE_TX_DESC(*tx_ring, ring_num);
-	tx_desc->buffer_addr = (buffer_info->dma);
-	tx_desc->length = (tmp_skb->len);
-	tx_desc->tx_words_eob = ((tmp_skb->len + 3));
+	tx_desc->buffer_addr = buffer_info->dma;
+	tx_desc->length = skb->len;
+	tx_desc->tx_words_eob = skb->len + 3;
 	tx_desc->tx_frame_ctrl = (frame_ctrl);
-	tx_desc->gbec_status = (DSC_INIT16);
+	tx_desc->gbec_status = DSC_INIT16;
 
 	if (unlikely(++ring_num == tx_ring->count))
 		ring_num = 0;
@@ -1265,7 +1276,6 @@  static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
 	pch_tx_timestamp(adapter, skb);
 #endif
 
-	dev_kfree_skb_any(skb);
 }
 
 /**
@@ -1543,19 +1553,12 @@  static void pch_gbe_alloc_tx_buffers(struct pch_gbe_adapter *adapter,
 					struct pch_gbe_tx_ring *tx_ring)
 {
 	struct pch_gbe_buffer *buffer_info;
-	struct sk_buff *skb;
 	unsigned int i;
-	unsigned int bufsz;
 	struct pch_gbe_tx_desc *tx_desc;
 
-	bufsz =
-	    adapter->hw.mac.max_frame_size + PCH_GBE_DMA_ALIGN + NET_IP_ALIGN;
-
 	for (i = 0; i < tx_ring->count; i++) {
 		buffer_info = &tx_ring->buffer_info[i];
-		skb = netdev_alloc_skb(adapter->netdev, bufsz);
-		skb_reserve(skb, PCH_GBE_DMA_ALIGN);
-		buffer_info->skb = skb;
+		buffer_info->skb = NULL;
 		tx_desc = PCH_GBE_TX_DESC(*tx_ring, i);
 		tx_desc->gbec_status = (DSC_INIT16);
 	}
@@ -1622,9 +1625,9 @@  pch_gbe_clean_tx(struct pch_gbe_adapter *adapter,
 					 buffer_info->length, DMA_TO_DEVICE);
 			buffer_info->mapped = false;
 		}
-		if (buffer_info->skb) {
-			pr_debug("trim buffer_info->skb : %d\n", i);
-			skb_trim(buffer_info->skb, 0);
+		if (skb) {
+			dev_kfree_skb_any(skb);
+			buffer_info->skb = NULL;
 		}
 		tx_desc->gbec_status = DSC_INIT16;
 		if (unlikely(++i == tx_ring->count))