netdev - Re: [PATCH][net-next] gianfar: Fix reported sent bytes to BQL for Tx timestamping

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Date:	Mon, 29 Apr 2013 08:28:35 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Claudiu Manoil <claudiu.manoil@...escale.com>
Cc:	netdev@...r.kernel.org,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH][net-next] gianfar: Fix reported sent bytes to BQL for
 Tx timestamping

On Mon, 2013-04-29 at 08:23 -0700, Eric Dumazet wrote:
> On Mon, 2013-04-29 at 17:27 +0300, Claudiu Manoil wrote:
> > 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;

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[]



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