On Fri 31 Jul 2009 03:46, Alessandro Rubini pondered:
For some reason - why I'm ping flooding when tftping a large file (with large tftp block size) - things hang. If I set the block size to under the MTU - it works fine. Do you get the same?
Didn't try, and I can't do that today. I suspect either your ping is over-mtu, so each new fragment triggers the above code,
No ping is the default length. The default packet size is 56 bytes, which translates into 98 bytes on the wire (8 bytes of ICMP header data, 20 for the IP header, and another 14 for the MAC addresses)
or simply your ether+uboot can't keep up with the data rate.
That doesn't explain, why does it work, when there is no fragmentation???
What it looks like is there is something wrong with the main network loop - the system is so busy responding to pings, that it never sends the TFTP Block ACK when it should.
As eaplained in the cover letter cover.1248943812.git.rubini@unipv.it some fragments can be lost in high traffic, as polling mode doesn't allow to enqueue packets. So I think you just loose some fragments, as target CPU time is eaten by the ping packets, and you don't get the complete reassembled packet any more.
I'm pretty sure it's like this.
I'm not convinced yet - but need to do some further poking on a different network...
On the other hand, I found a minor issue in this situation:
- start a tftp transfer
- ctrl-C it
- start another
Server retransmissions for the first transfer go into the defrag engine e that reset-defrag-data code is triggered, so a packet may be lost, and I get a sporadic T in the receiving u-boot. I think it's not a real problem, though --- or, now that I rethink about it, it can be the same issue as above: my ether can't enqueue 8k of stuff so a fragment is lost in that case.
What is missing in the reassembly code (that is described in RFC815) is the timer. (quote from the RFC): -------------- The final part of the algorithm is some sort of timer based mechanism which decrements the time to live field of each partially reassembled datagram, so that incomplete datagrams which have outlived their usefulness can be detected and deleted. --------------