Re: [uCsimm] cat and telnet performance problems

From: Vladimir Gurevich (
Date: Wed Jan 05 2000 - 16:52:38 EST


Sometime ago I posted a message about performance problems when cat
is run in a telnet session:

"Vladimir A. Gurevich" wrote:

> While "cat" works perfectly
> on the console now (the output is quick and smooth), it does not work
> that well over telnet connection. The output happens in bursts and one
> can easily observe long delays between them. I tried to use tcpdump
> to see what was going on and noticed, that wor some reason the write()
> call usually returns about 1-2 seconds after uClinux receives TCP ACK
> for the corresponding packet. Since there are too many layers involved
> (telnetd, PTY code, socket code, ethernet driver) this problem will
> probably take some time to resolve. Since I can observe the same
> behaviour on both PPP and Ethernet links I would probably exclude
> ethernet driver for now.

Looks like this is a common problem with TCP socket code. I have some
other programs that write directly into a TCP socket and experience the
same kind of "bursted" output regardless of whether Ethernet or PPP is
used. Since telnetd is not involved there, all PTY code and telnetd
are not suspected anymore.

I did a quick look, but could not find any uClinux-specific stuff in the
socket code.

Any ideas what might be broken?


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