LARTC - Dec 2001 - Subject: Re: SFQ + RED

After an off-list discussion I think Martin now agrees with me that
sfq will not let one large flow deny service to all others.
It''s actually the other way around, ensuring service to the small ones
even at the expense of the large ones.

 > From: Martin Devera <devik@cdi.cz>
 > 
 > IMHO the RED would be useful here. SFQ limits total packet count
 > to 128 packets. So that one flow can simply fill whole SFQ leaving
 > small space for other flows.
 > I''m able to simulate it using one host generating huge UDP flow.
 > All others flow goes away :(
 > 
 > devik 
 > 
 > On Mon, 3 Dec 2001, Don Cohen wrote:
 > 
 > > 
 > >  > On Tue, Nov 27, 2001 at 11:53:10AM -0500, Michael T. Babcock
wrote:
 > >  > > I''ve asked this before, but does anyone feel
technically inclined
 > >  > > enough to try swapping in a RED queue for the per-bucket
queuing done
 > >  > > by SFQ?  If SFQ builds a series of
''sessions'' to be given fair use of
 > >  > > available bandwidth, using RED to slow down those that are
building up
 > >  > > too fast would smooth things out.
 > > 
 > > I don''t think this is necessary.  As it is now, when you
enqueue a
 > > packet in a full SFQ queue it drops from the tail of the longest
 > > subqueue.  If you have substantial competition for the link then
 > > your subqueue won''t be allowed to grow very long to begin
with.
 > > The random variation in demand from other flows will have the effect
 > > of jittering the maximum length of your subqueue, which is pretty
 > > similar to what you experience with RED, isn''t it?

yes I do. I oversight the sfq_drop call in enqueue ;-)
devik

On Fri, 7 Dec 2001, Don Cohen wrote:
> 
> After an off-list discussion I think Martin now agrees with me that
> sfq will not let one large flow deny service to all others.
> It''s actually the other way around, ensuring service to the small
ones
> even at the expense of the large ones.
> 
>  > From: Martin Devera <devik@cdi.cz>
>  > 
>  > IMHO the RED would be useful here. SFQ limits total packet count
>  > to 128 packets. So that one flow can simply fill whole SFQ leaving
>  > small space for other flows.
>  > I''m able to simulate it using one host generating huge UDP
flow.
>  > All others flow goes away :(
>  > 
>  > devik 
>  > 
>  > On Mon, 3 Dec 2001, Don Cohen wrote:
>  > 
>  > > 
>  > >  > On Tue, Nov 27, 2001 at 11:53:10AM -0500, Michael T.
Babcock wrote:
>  > >  > > I''ve asked this before, but does anyone feel
technically inclined
>  > >  > > enough to try swapping in a RED queue for the
per-bucket queuing done
>  > >  > > by SFQ?  If SFQ builds a series of
''sessions'' to be given fair use of
>  > >  > > available bandwidth, using RED to slow down those
that are building up
>  > >  > > too fast would smooth things out.
>  > > 
>  > > I don''t think this is necessary.  As it is now, when
you enqueue a
>  > > packet in a full SFQ queue it drops from the tail of the longest
>  > > subqueue.  If you have substantial competition for the link then
>  > > your subqueue won''t be allowed to grow very long to
begin with.
>  > > The random variation in demand from other flows will have the
effect
>  > > of jittering the maximum length of your subqueue, which is
pretty
>  > > similar to what you experience with RED, isn''t it?
> 
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