Re: [lwip-users] losing input packets and repeated acks

[Carl D. Blake]

On Mon, 2007-01-15 at 10:48, Jonathan Larmour wrote:
> > I made the changes you suggested and things are a little better.  I'm
> > still getting the huge delay periodically, but the multiple acks of the
> > same packet and the same window size are gone.  I still get multiple
> > acks of the same packet, but the system seems to be advertising a larger
> > window size for each ack.  I seem to be getting some corrupt data, but
> > it's not nearly as bad as it was before.
> 
> Missing data is one thing, but corrupt data implies to me that there is 
> something more problematic going on at a lower level, possibly hardware, 
> more likely your software ethernet device driver.
> 
Hmmm.  I'll look at this possibility more closely.

> > I enabled LWIP_STATS and printed out the stats before and after the
> > transfer.  TCP stats is reporting several checksum errors.  PBUF stats
> > is reporting several errors.  I enabled debug messages for pbufs and I'm
> > getting the message "pbuf_alloc: Out of pbufs in pool."  This happens
> > quite a bit during the transfer of 1 Mbyte.  I hadn't expected this to
> > be a problem since my pbuf memory is 45Kbytes and my TCP window is
> > 16Kbytes.  Any other suggestions?
> 
> Indeed the remote side should not send more data than the receive window, 
> although it may use up a few more pbufs with things like acks. I guess you 
> could try and find out where the pbufs are going - it's possible your 
> driver might be leaking pbufs. When the stack goes back to quiescent, do 
> the stats return to the starting state? i.e. record stats, exchange lots of 
> data for a bit, stop exchanging data, record stats again.
> 
When the stack is quiescent the stats return to the starting state.  The
PBUF stats show 90 available and 0 used.  I don't think I'm leaking
pbufs.

> Jifl