netdev - Re: [PATCH] sched: QFQ - quick fair queue scheduler (v4)

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Message-ID: <20110304091859.395f2752@nehalam>
Date:	Fri, 4 Mar 2011 09:18:59 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Luigi Rizzo <rizzo@....unipi.it>, netdev@...r.kernel.org
Subject: Re: [PATCH] sched: QFQ - quick fair queue scheduler (v4)

On Fri, 04 Mar 2011 07:50:26 +0100
Eric Dumazet <eric.dumazet@...il.com> wrote:

> Le jeudi 03 mars 2011 à 16:30 -0800, Stephen Hemminger a écrit :
> > This is an implementation of the Quick Fair Queue scheduler developed
> > by Fabio Checconi. The same algorithm is already implemented in ipfw
> > in FreeBSD. Fabio had an earlier version developed on Linux, I just
> > cleaned it up.  Thanks to Eric Dumazet for doing the testing and
> > finding bugs.
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> > 
> > ---
> > v4 - change slots[] to hlist from simple linked list
> > 
> >  include/linux/pkt_sched.h |   15 
> >  net/sched/Kconfig         |   11 
> >  net/sched/Makefile        |    1 
> >  net/sched/sch_qfq.c       | 1133 ++++++++++++++++++++++++++++++++++++++++++++++
> >  4 files changed, 1160 insertions(+)
> 
> Thanks
> 
> Still crashing hard here in qfq_reset_qdisc(), when packets are present
> in queues.
> 
> Probably hlist_for_each_entry_safe() is needed, since
> qfq_deactivate_class() is called ...
> 
> Also rename cl->next to cl->hnode so that following is clearer ?
> 
> -	hlist_for_each_entry(cl, n, &grp->slots[j], next) {
> +	hlist_for_each_entry_safe(cl, n, next, &grp->slots[j], hnode) {
> 
> Fabio, any idea why everything is blocked after a few packets for me ?
> 
> Here is script to reproduce the problem :
> 
> # cat qfq_setup.sh
> modprobe dummy
> 
> ifconfig dummy0 10.2.2.254 netmask 255.255.255.0 up
> 
> for i in `seq 1 16`
> do
>  arp -H ether -i dummy0 -s 10.2.2.$i 00:00:0c:07:ac:$(printf %02x $i)
> done
> 
> DEV=dummy0
> RATE="rate 40Mbit"
> TNETS="10.2.2.0/25"
> ALLOT="allot 20000"
> 
> tc qdisc del dev dummy0 root 2>/dev/null
> 
> tc qdisc add dev $DEV root handle 1: cbq avpkt 1000 rate 1000Mbit \
> 	bandwidth 1000Mbit

QFQ is non work conserving, it may choose to send a smaller packet
ahead of a larger packet in other flow...


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