[En-Nut-Discussion] TCP vs. Memory - a solution

[Harald Kipp]

OK, OK! I got it. :-)

I added NutSleep(5000) into Nut's loop.

On the remote I sent the first buffer byte only and added a Sleep(1) to
give TCP more time to process the small packet.

After a short time Nut/OS heap space went down to 82 bytes. Wow!

Interestingly, after a few more packets the situation becomes more
stable and heap allocation didn't increase more than 10k. I agree, that
this is still a lot.

Harald


Harald Kipp wrote:
> Michael Jones wrote:
>> This, proof of concept change seems to work:
> 
> before considering to apply your change I'd like to test it here.
> However, I failed to reproduce the problem.
> 
> As you wrote, the remote peer will fill up the our local memory with
> packets. But how can this be? Ethernut announces its TCP window size and
> the remote will never send more than this amount without further ACK.
> 
> Nut/OS 4.9 announces a TCP window size of 3216 bytes. The remote (PC
> running Windows 2003) runs something like
> 
> for(n = 0; ; n++) {
>  sprintf(buffer, "%lu\n", n);
>  send(sock, buffer, (int)strlen(buffer), 0);
> }
> 
> and Nut/OS uses
> 
> for (;;) {
>  NutTcpReceive(sock, buffer, sizeof(buffer));
> }
> 
> Both loops are simplified. Actually I'm checking results and doing some
> debug output.
> 
> Wireshark shows
> 
> PC: 2 bytes
> Nut: ACK (win=3214)
> PC: 132 bytes
> PC: 6 bytes
> Nut: ACK (win=3076)
> 
> ...and so on. After a short time, as expected
> 
> Nut: ACK (win=570)
> PC: 228 bytes
> Nut: ACK (win=0)
> Nut: ACK (win=598)
> PC: 536 bytes
> Nut: ACK (win=0)
> 
> Nut's memory never drops by more than 5k.
> 
> May be I have to find a way to force the PC to send smaller packets. But
> how? As soon as Nut closes the window, the remote will collect all data
> into one packet. When Nut opens the window again, the remote will send
> the maximum in one packet. This maximum is limited by the newly
> announced window size and the MSS.
> 
> Any idea how to reproduce the problem?
> 
> Harald
> 
> P.S.: I do remember the discussion about the zero window size problem
> eating up all memory, which appeared here earlier and I'll look into
> this as well.
> 
> 
> _______________________________________________
> http://lists.egnite.de/mailman/listinfo/en-nut-discussion


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