On 4/29/2013 6:28 PM, Eric Dumazet wrote:

On Mon, 2013-04-29 at 08:23 -0700, Eric Dumazet wrote:

quoted

On Mon, 2013-04-29 at 17:27 +0300, Claudiu Manoil wrote:

quoted

Hi,

Unfortunately fixing this the other way around would imply changes
in both xmit and clean_tx, and additional overhead in clean_tx.
On xmit skb->len gets incremented with FCB_LEN and/or TXPAL_LEN,
on a case by case basis. This would imply to add extra checks on
clean_tx to identify whether only FCB_LEN has been added, or
FCB+TXPAL or neither, all these just to report the bytes on wire
for BQL.
Does BQL really need to measure the bytes-on-wire or the bytes consumed
for buffering?

Yes.

What about :

diff --git a/drivers/net/ethernet/freescale/gianfar.c b/drivers/net/ethernet/freescale/gianfar.c
index 2375a01..bb727e1 100644
--- a/drivers/net/ethernet/freescale/gianfar.c
+++ b/drivers/net/ethernet/freescale/gianfar.c

@@ -2065,6 +2065,7 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
  	u32 bufaddr;
  	unsigned long flags;
  	unsigned int nr_frags, nr_txbds, length, fcb_length = GMAC_FCB_LEN;
+	unsigned int len;

  	/* TOE=1 frames larger than 2500 bytes may see excess delays
  	 * before start of transmission.

@@ -2130,7 +2131,8 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
  	}

  	/* Update transmit stats */
-	tx_queue->stats.tx_bytes += skb->len;
+	len = skb->len;

Already tried this change in xmit, but it breaks the UDP/TCP cases (eg. 
ftp). Due to (skb->ip_summed == CHECKSUM_PARTIAL) condition FCB is
added on xmit (skb->len increased with FCB_LEN only), and Tx completion
does not make this check.

Idea is to use this value in TX completion.

If at tx completion skb->len might be different, then store the true
skb->len in skb->cb[]

Interesting but non-trivial, I think. Is this allowed? I mean, doesn't
the net stack overwrite this field?

Thanks,
Claudiu