netdev - Re: Bug#565404: linux-image-2.6.26-2-amd64: atl1e: TSO is broken

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Date:	Tue, 02 Apr 2013 15:34:53 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	"Huang, Xiong" <xiong@....qualcomm.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Anders Boström <anders@...insight.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"565404@...s.debian.org" <565404@...s.debian.org>
Subject: Re: Bug#565404: linux-image-2.6.26-2-amd64: atl1e: TSO is broken

On Wed, 2013-04-03 at 00:15 +0200, Hannes Frederic Sowa wrote:
> On Tue, Apr 02, 2013 at 03:00:38PM -0700, Eric Dumazet wrote:
> > On Tue, 2013-04-02 at 23:15 +0200, Hannes Frederic Sowa wrote:
> > 
> > > The error vanishes as soon as I put a gso size limit of MAX_TX_BUF_LEN
> > > in the driver. MAX_TX_BUF_LEN seems to be arbitrary set to 0x2000. I
> > > can even raise it to 0x3000 and don't see any tcp retransmits. Do you
> > > have an advice on how to size this value (e.g. should we switch to the
> > > windows values)?
> > 
> > This looks like an overflow error...
> 
> Thanks for your input, Eric.
> 
> I am limited in my time to work on this today but nontheless just tested
> your patch without any of my changes and count a lot of TcpRetransSegs
> again. Either there is really some hardware limitation or another
> overflow.

Another overflow...

Really I don't understand why people use u16 instead of u32.

u16 is slower most of the time, and more prone to overflows.

diff --git a/drivers/net/ethernet/atheros/atl1e/atl1e_main.c b/drivers/net/ethernet/atheros/atl1e/atl1e_main.c
index 7e0a822..48ac487 100644
--- a/drivers/net/ethernet/atheros/atl1e/atl1e_main.c
+++ b/drivers/net/ethernet/atheros/atl1e/atl1e_main.c
@@ -1569,18 +1569,17 @@ static u16 atl1e_cal_tdp_req(const struct sk_buff *skb)
 {
 	int i = 0;
 	u16 tpd_req = 1;
-	u16 fg_size = 0;
-	u16 proto_hdr_len = 0;
 
 	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
-		fg_size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
+		u32 fg_size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
+
 		tpd_req += ((fg_size + MAX_TX_BUF_LEN - 1) >> MAX_TX_BUF_SHIFT);
 	}
 
 	if (skb_is_gso(skb)) {
 		if (skb->protocol == htons(ETH_P_IP) ||
 		   (skb_shinfo(skb)->gso_type == SKB_GSO_TCPV6)) {
-			proto_hdr_len = skb_transport_offset(skb) +
+			u32 proto_hdr_len = skb_transport_offset(skb) +
 					tcp_hdrlen(skb);
 			if (proto_hdr_len < skb_headlen(skb)) {
 				tpd_req += ((skb_headlen(skb) - proto_hdr_len +
@@ -1670,7 +1669,7 @@ static void atl1e_tx_map(struct atl1e_adapter *adapter,
 {
 	struct atl1e_tpd_desc *use_tpd = NULL;
 	struct atl1e_tx_buffer *tx_buffer = NULL;
-	u16 buf_len = skb_headlen(skb);
+	u32 buf_len = skb_headlen(skb);
 	u16 map_len = 0;
 	u16 mapped_len = 0;
 	u16 hdr_len = 0;


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