[ros-dev] Loopback problem
Ge van Geldorp
gvg at reactos.org
Wed Dec 21 11:08:09 CET 2005
> From: Phillip Susi
> The entire point of having a window is so that the sender can send
> multiple packets before the first is ACK'd. Are you sure that the
> existing code refuses to send even when the window should
> allow it?
I've been wrong before, but that's my interpretation of what's happening.
We've only sent one byte and are trying to send another single byte.
> Or is the window just too small?
Since a window size of 1 doesn't make sense, the window size must be big
enough. I believe it is actually 16384, plenty of room for the 2 bytes we've
sent/are trying to send.
> From: art yerkes
> The problem is likely in our loopback pseudo adapter rather
> than the BSD code, I'd guess.
Please don't take this the wrong way (I'm still impressed by the work you
and Casper did on integrating the network stack), but that was my initial
thought too... However, as far as I can see the second send just doesn't
make it to the loopback adapter, it's tcp_output() which decides it
shouldn't be sent.
> It actually doesn't come directly from BSD. It was first in
> oskit, in which some work was done to isolate a few parts of
> FreeBSD and simplify and generalize the buffer management
> code. If there's a mistake in the TCP implementation itself,
> I might have introduced it.
I checked the FreeBSD code and there seems to be a fix in there (which is
not present in our tree) related to this
"Add a flag TF_LASTIDLE, that forces a previously idle connection
to send all its data, especially when the data is less than one MSS.
This fixes an issue where the stack was delaying the sending
of data, eventhough there was enough window to send all the data and
the sending of data was emptying the socket buffer."
That same TF_LASTIDLE flag is also present in OpenBSD (not surprising, since
they say they imported it from FreeBSD). I'll see if I can apply the same
change to our tree.
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