netdev - Re: [PATCH] CHOKe flow scheduler (0.8)

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Date:	Fri, 14 Jan 2011 04:34:27 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] CHOKe flow scheduler (0.8)

Le vendredi 14 janvier 2011 à 04:29 +0100, Eric Dumazet a écrit :
> Le jeudi 13 janvier 2011 à 15:34 -0800, Stephen Hemminger a écrit :
> > CHOKe ("CHOose and Kill" or "CHOose and Keep") is an alternative
> > packet scheduler based on the Random Exponential Drop (RED) algorithm.
> > 
> > The core idea is:
> >   For every packet arrival:
> >   	Calculate Qave
> > 	if (Qave < minth) 
> > 	     Queue the new packet
> > 	else 
> > 	     Select randomly a packet from the queue 
> > 	     if (both packets from same flow)
> > 	     then Drop both the packets
> > 	     else if (Qave > maxth)
> > 	          Drop packet
> > 	     else
> > 	       	  Admit packet with probability P (same as RED)
> > 
> > See also:
> >   Rong Pan, Balaji Prabhakar, Konstantinos Psounis, "CHOKe: a stateless active
> >    queue management scheme for approximating fair bandwidth allocation", 
> >   Proceeding of INFOCOM'2000, March 2000.
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> > 
> > ---
> > 0.8 change queue length and holes account.
> >     keep sch->q.qlen updated, and holes counter not needed.
> > 
> > ---
> >  net/sched/Kconfig     |   11 +
> >  net/sched/Makefile    |    1 
> >  net/sched/sch_choke.c |  536 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 548 insertions(+)
> > 
> 
> Hi Stephen
> 
> Your diffstat was an old one, here the right one.
> 
>  include/linux/pkt_sched.h |   29 +
>  net/sched/Kconfig         |   11 
>  net/sched/Makefile        |    1 
>  net/sched/sch_choke.c     |  552 ++++++++++++++++++++++++++++++++++++
> 
> 
> I tested v8 and found several serious problems, please find a diff of my
> latest changes :
> 
> - wrong oskb/skb used in choke_enqueue()
> - choke_zap_head_holes() is called from choke_dequeue() and crash if we
> dequeued last packet. (!!!)
> - out of bound access in choke_zap_tail_holes()
> - choke_dequeue() can be shorter
> - choke_change() must dequeue/drop in excess packets or risk new array
> overfill (if we reduce queue limit by tc qdisc change ...)
> - inline is not needed, space errors in include file
> 
> Thanks !

Hmm, please wait a bit, I had another crash when I stopped my
bench/stress



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