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Date: Tue, 05 Mar 2002 13:17:42 -0800
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From: Maksim Krasnyanskiy <maxk@qualcomm.com>
Subject: Re: PPP feature request (Tx queue len + close)
Cc: Paul Mackerras <paulus@samba.org>, linux-ppp@vger.kernel.org,
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> > effectively makes your window equal to 1 segment. In any case small PPP
> > queue won't make any good for you.
>
>         Nope. Remember that I have buffers below PPP. The transmit
>path within PPP and IrNET is minimal (no framing), so buffers in PPP
>and below PPP are logically equivalent.
True. PPP is a sort of "pass through" thing in your case.

> > I was under assumption that you know for sure that buffering is bad for 
> you :)
>
>         We are running circles. I want to reduce the amount of buffers
>below TCP. This includes PPP buffers and buffers below PPP (both are
>logically equivalent).
>         Both of you are saying "increase buffers at PPP level and
>reduce below TCP", but this doesn't make sense, and that's what I was
>pointing out. You have to think on the whole stack, not each
>individual component.
Yes. I see your point. It doesn't really make any difference which layer
buffers stuff (unless that layer introduces delays). So I guess in your case
you can just set txqueuelen to 1 if you're sure that underlying layer has long
enough queues.

> > All this depends on what you want to achieve. If you're looking for max TCP
> > performance. I'd recommend to use tcptrace and see what actually is 
> going on.
> > May be your RTT is to high and you need bigger windows or may be there is
> > something else.
>
>         I get 3.2 Mb/s TCP throughput over a 4Mb/s IrDA link layer, so
>I'm not concernet with max performance. My question is more "how much
>buffers can I trim without impacting performance". The goal is to
>improve latency and decrease ressource consumption.
I see.
Did you try ifconfig txqueuelen 1 ?

Max

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