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Subject: Re: [PATCH v2] net: add Faraday FTMAC100 10/100 Ethernet driver
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Ben Hutchings <bhutchings@solarflare.com>
Cc: Po-Yu Chuang <ratbert.chuang@gmail.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, ratbert@faraday-tech.com,
        joe@perches.com, dilinger@queued.net
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Date: Mon, 17 Jan 2011 21:39:32 +0100
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Le lundi 17 janvier 2011 à 18:58 +0000, Ben Hutchings a écrit :
> On Mon, 2011-01-17 at 18:29 +0100, Eric Dumazet wrote:
> > Le lundi 17 janvier 2011 à 17:21 +0800, Po-Yu Chuang a écrit :
> > 
> > 
> > > +static int ftmac100_rx_packet(struct ftmac100 *priv, int *processed)
> > > +{
> > > +	struct net_device *netdev = priv->netdev;
> > > +	struct ftmac100_rxdes *rxdes;
> > > +	struct sk_buff *skb;
> > > +	int length;
> > > +	int copied = 0;
> > > +	int done = 0;
> > > +
> > > +	rxdes = ftmac100_rx_locate_first_segment(priv);
> > > +	if (!rxdes)
> > > +		return 0;
> > > +
> > > +	length = ftmac100_rxdes_frame_length(rxdes);
> > > +
> > > +	netdev->stats.rx_packets++;
> > > +	netdev->stats.rx_bytes += length;
> > > +
> > > +	if (unlikely(ftmac100_rx_packet_error(priv, rxdes))) {
> > > +		ftmac100_rx_drop_packet(priv);
> > > +		return 1;
> > > +	}
> > > +
> > > +	/* start processing */
> > > +	skb = netdev_alloc_skb_ip_align(netdev, length);
> > > +	if (unlikely(!skb)) {
> > > +		if (net_ratelimit())
> > > +			netdev_err(netdev, "rx skb alloc failed\n");
> > > +
> > > +		ftmac100_rx_drop_packet(priv);
> > > +		return 1;
> > > +	}
> > > +
> > 
> > Please dont increase rx_packets/rx_bytes before the
> > netdev_alloc_skb_ip_align().
> > 
> > In case of mem allocation failure, it would be better not pretending we
> > handled a packet.
> >
> > drivers/net/r8169.c for example does the rx_packets/rx_bytes only if
> > packet is delivered to upper stack.
> 
> That's news to me.  I specifically advised Po-Yu Chuang to increment
> these earlier because my understanding is that all packets/bytes should
> be counted.  And drivers which use hardware MAC stats will generally do
> that, so I really don't think it makes sense to make other drivers
> different deliberately.
> 

I see, but when one frame is dropped because of RX ring buffer
under/overflow we dont account for the lost packet/bytes.

Thats probably not very important, but would be good if all drivers
behave the same.