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

[Hannes Frederic Sowa <hannes@stressinduktion.org>]

On Tue, Apr 02, 2013 at 03:34:53PM -0700, Eric Dumazet wrote:
> 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.

Just gave your patch a test and I still have a fast increasing tcp
retransmitted segments counter.

Maximum skb length hitting the device is 23234 in my tests (as reported
by ftrace). So I actually think it is a device limitation.