Subject: Re: multilink
To: <>
From: Ignatios Souvatzis <>
List: tech-net
Date: 06/05/2000 10:07:52
On Thu, Jun 01, 2000 at 10:18:37AM +0100, Brian Somers wrote:
> > On Wed, May 31, 2000 at 01:07:22AM +0100, Brian Somers wrote:
> > 
> > > User-ppp will do MP without any noticeable loss in performance. ...
> > 
> > ...for fast CPUs and slow links.
> To an extent, yes.  I can get 1.5 Mb (bytes, not bits) through a 
> synchronous back-to-back user-ppp connection on my laptop (PII366) 
I notice this number...
> with compression disabled.
... and this restriction.

at what %CPU usage, and what context switch rate?

> Also, I'd argue that on an SMP box, user-land MP ppp will beat the 
> socks off any kernel implementation - at least for the forseeable 
> (disclaimer: I know nothing about NetBSD SMP mutexes !!).  Especially 
> when you introduce compression - usually better done in userland.

Not necessarily. We're already doing it at a low priority software interupt,
and I guess we could move it to a kernel thread now. Besides: if you're doing
it in userland, you'll get an increasing context switch rate if you have (due
to your increasing CPU capabilities) an increasing data rate (packet sizes are
limited). So you'll be limited by context switching abilities of your hardware
(CPU, caches, translation tables), not by CPU power per se.

You're talking about machines with 10^3 to 10^4 times the CPU power of
the low-end NetBSD machines, and about 50 times the memory. You'll always
have a class of links for a given class of machines where userland PPP is
ok... and you'll always have another class where it doesn't really work.

So you should mention the details of your setup, if you're publishing claims

> > > User-ppp will do MP without any noticeable loss in performance. ...

which is certainly true for fast modem to ISDN/double ISDN speeds on most of
the supported machines... but not for every supported (by NetBSD) combination.

Of course, if you want to do multilink PPP, you have no choice currently.